Stoyan, Ronald - Atlas of the Messier Objects
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Atlas of the Messier Objects Highlights of the Deep Sky The 110 star clusters, nebulae and galaxies of Messier’s catalog are among the most popular of all the deep sky objects and are beautiful targets for amateur observers of all abilities. This new atlas presents a complete account of all of the Messier objects, detailing, for each object: • • • •
its astrophysical significance well-researched background on its discovery clear observational descriptions from naked eye through to large telescopes observations and anecdotes from Messier himself and other famous observers from the past
In addition, this atlas has some of the world’s finest color astrophotos, inverted photos that have been labeled to point to hidden details and neighboring objects, and historical sketches alongside new deep sky drawings, helping to bring the Messier objects to life. Painting an engaging portrait of Charles Messier’s life and observations, this is the most far-reaching and beautiful reference on the Messier objects there has ever been, and one that no observer should be without!
RONALD STOYAN is editor-in-chief of interstellarum, one of Germany’s main astronomy magazines. He was the founding director of the German deep sky organization ‘Fachgruppe Deep-Sky’, and has authored and coauthored six books on practical astronomy. STEFAN BINNEWIES is a leading astrophotographer and travels around the world to get the best shots. He has
worked on several amateur observatory projects, including helping to establish the Capella Observatory near Windhoek, Namibia. SUSANNE FRIEDRICH is an editor for interstellarum and a visiting scientist at Max-Planck-Institute for extraterrestrial physics. A trained astrophysicist, she has been observing the sky both visually and photographically for more than 25 years. KLAUS-PETER SCHROEDER is Professor of Astronomy at the University of Guanajauto, Mexico. An avid amateur
astronomer and photographer since youth, he has published several books on astrophotography and is a regular contributor writing for amateur astronomy magazines.
Cover illustration: A majestic view of M 31, M 32, and M 110, our intergalactic neighbors. This image was taken by Robert Gendler in September and November, 2005. A 20-inch reflector was used at 4000mm focal length, total exposure was 90 hours with a SBIG CCD camera STL-11000XM, from Nighthawk Observatory, New Mexico, USA.
ATLAS of the
MESSIER OBJECTS HIGHLIGHTS OF THE DEEP SKY Ronald Stoyan Stefan Binnewies, Susanne Friedrich and Klaus-Peter Schroeder
CAMBRIDGE UNIVERSITY PRESS
Cambridge, New York, Melbourne, Madrid, Cape Town, Singapore, São Paulo Cambridge University Press The Edinburgh Building, Cambridge CB2 8RU, UK Published in the United States of America by Cambridge University Press, New York www.cambridge.org Information on this title: www.cambridge.org/9780521895545 © Cambridge University Press 2008 This publication is in copyright. Subject to statutory exception and to the provision of relevant collective licensing agreements, no reproduction of any part may take place without the written permission of Cambridge University Press. First published in print format 2008
ISBN-13 978-0-511-42329-1
eBook (EBL)
ISBN-13
hardback
978-0-521-89554-5
Cambridge University Press has no responsibility for the persistence or accuracy of urls for external or third-party internet websites referred to in this publication, and does not guarantee that any content on such websites is, or will remain, accurate or appropriate.
Dedicated to the memory of my brother Norman Stoyan (1975–2003)
Table of contents Table of contents Foreword Preface User guide
6 8 9 10
Charles Messier The Observations The Catalog Statistics of the Messier objects Visual observation of the Messier objects Photography of the Messier objects
15 25 39 53 63 68
The 110 Messier objects
71
Glossary of technical terms Index of figures Index of sources
6
357 362 365
Object
Type
Constellation
M M M M M M M M
1 2 3 4 5 6 7 8
Taurus Aquarius Canes Venatici Scorpius Serpens Scorpius Scorpius Sagittarius
M M M M M M M M M M M M M M M M M M M M M M M M M M M M M M M
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39
Galactic nebula Globular cluster Globular cluster Globular cluster Globular cluster Open cluster Open cluster Galactic nebula and Open cluster Globular cluster Globular cluster Open cluster Globular cluster Globular cluster Globular cluster Globular cluster Open cluster Galactic nebula Open cluster Globular cluster Galactic nebula Open cluster Globular cluster Open cluster Star cloud Open cluster Open cluster Planetary nebula Globular cluster Open cluster Globular cluster Galaxy Galaxy Galaxy Open cluster Open cluster Open cluster Open cluster Open cluster Open cluster
Ophiuchus Ophiuchus Scutum Ophiuchus Hercules Ophiuchus Pegasus Serpens Sagittarius Sagittarius Ophiuchus Sagittarius Sagittarius Sagittarius Sagittarius Sagittarius Sagittarius Scutum Vulpecula Sagittarius Cygnus Capricornus Andromeda Andromeda Triangulum Perseus Gemini Auriga Auriga Auriga Cygnus
Page 71 76 78 80 82 84 86 88 93 95 96 98 100 104 106 108 111 115 116 117 122 124 126 128 131 132 134 139 140 142 144 152 153 158 160 162 164 166 168
Object
Type
Constellation
Page
Object
Type
Constellation
Page
M M M M M M M M M M M M M M M M M M M M M M M M M M M M M M M M M M M M M M M M
Optical double star Open cluster Galactic nebula Galactic nebula Open cluster Open cluster Open cluster Open cluster Open cluster Galaxy Open cluster Galaxy Open cluster Globular cluster Globular cluster Globular cluster Globular cluster Planetary nebula Galaxy Galaxy Galaxy Galaxy Globular cluster Galaxy Galaxy Galaxy Galaxy Open cluster Globular cluster Globular cluster Globular cluster Globular cluster Globular cluster Asterism Galaxy Globular cluster Planetary nebula Galaxy Galactic nebula Globular cluster
Ursa Major Canis Major Orion Orion Cancer Taurus Puppis Puppis Hydra Virgo Monoceros Canes Venatici Cassiopeia Coma Sagittarius Sagittarius Lyra Lyra Virgo Virgo Virgo Virgo Ophiuchus Canes Venatici Coma Leo Leo Cancer Hydra Sagittarius Sagittarius Sagitta Aquarius Aquarius Pisces Sagittarius Perseus Cetus Orion Lepus
170 171 173 183 184 187 193 195 197 199 201 203 208 210 212 213 215 217 224 226 228 230 233 235 238 241 245 248 250 252 253 254 256 258 259 262 264 266 269 272
M M M M M M M M M M M M M M M M M M M M M M M M M M M M M M M
Globular cluster Galaxy Galaxy Galaxy Galaxy Galaxy Galaxy Galaxy Galaxy Galaxy Galaxy Galaxy Globular cluster Open cluster Galaxy Galaxy Galaxy Planetary nebula Galaxy Galaxy Galaxy Galaxy Galaxy Open cluster Galaxy Galaxy Galaxy Globular cluster Galaxy Galaxy Galaxy
Scorpius Ursa Major Ursa Major Hydra Virgo Coma Virgo Virgo Coma Virgo Virgo Coma Hercules Puppis Canes Venatici Leo Leo Ursa Major Coma Coma Coma Ursa Major Draco Cassiopeia Virgo Leo Canes Venatici Ophiuchus Ursa Major Ursa Major Andromeda
273 276 280 283 287 290 292 294 297 299 302 305 307 309 310 313 315 318 321 323 326 329 333 336 338 341 344 347 348 351 353
40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79
80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110
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Foreword David H. Levy Why yet another Messier catalog book? With Kenneth Glyn-Jones,
What if Messier were to return to our time? He would be amazed
Stephen James O’Meara, and Ken Graun, haven’t we had enough?
at the ease by which visual comet hunting can be done, as well as the
No, I say! And especially no when the latest addition to the canon is
increased difficulty in finding a comet when well-funded electronic
Ronald Stoyan’s scholarly, historical, astrophysical, and superb look at
searches compete with amateur astronomers. With a computer star
the great comet hunter and the list of objects he compiled during his
chart riding with my telescope, I know instantly what my telescope is
lifetime.
showing at any particular moment. On the morning of October 2, 2006,
This book is the first scholarly look at the catalog since Glyn-Jones,
for example, the chart showed a rich field of stars with the planet Sa-
and that effort is almost half a century old. Stoyan explores the latest
turn in the field center; it did not display, however, the faint fuzzy spot
astrophysical research concerning each of Messier’s 110 deep sky ob-
that turned out to be my 22nd comet discovery, a new comet that will
jects. Stoyan could well devote his entire book to the astrophysics of
make a close approach to the Earth when it returns at the end of 2011.
Messier’s first object, the Crab Nebula, and I still subscribe to the belief
Messier obviously did not have such technology at his disposal; he used
that I read years ago that astronomy has two parts: that of the Crab and
his telescope and a printed star atlas, trusted friends that remained the
that of everything else. From the first time I looked at M 1 on September
classic way to search the sky until just a few years ago.
1, 1963, I’ve been fascinated by the ghostly luminescence of the Crab,
For all of Messier’s brilliance, his famous catalog was primarily an
but never more so than when it seemed ablaze again not with a new
observing tool, and Stoyan’s writing confirms this crucial footnote to
supernova, but with nearby Saturn visiting at nearly the same spot from
history: by keeping a record of the objects that could be mistaken for
which the original star first became visible on July 4, 1054.
comets, Messier provides himself and posterity an invaluable resource.
Next comes the historical view: I cannot get enough of the life
The pages you are about to read delve further into what his list looks
of Charles Messier, who lived, observed, searched, and suffered some
like after 200 years, and particularly the astrophysics that lies behind
two hundred years ago. This observer’s life story is compelling, and
each of the clusters, nebulae, and remote galaxies that constitute it.
Stoyan’s retelling adds new material. Although he was not the first
Stoyan does not take a position on one of the questions of our time –
person to discover a comet with a telescope, Messier was most likely
should the double cluster in Perseus be added to the list?
the first to organize a successful survey program specifically devoted
Yes, there is a need for “yet another” Messier catalog book. Stoyan
to the search for comets. For that accomplishment he certainly deser-
has done a masterful job giving his readers a modern look at Messier’s
ves a place with the greats like William Herschel, Kaoru Ikeya, and
greatest accomplishment. May this book inspire you to learn about the
Leslie Peltier. In Stoyan’s biographical summary we learn a little more
man and his project, and more importantly, may it encourage you to
about Messier’s famous accident, in which he fell into a pit. Although
don a coat, grab a telescope, and enjoy this window into the deep sky
he recovered enough to resume his work, we know for the first time
for yourself.
that he never completely got well again, and he finished his life with a continuing limp. A fortunate fall, to be sure, for he is lucky to have survived it in the first place.
8
Preface
The catalog gathered by the French astronomer Charles Messier (1730–1817) has been the most popular compilation of astronomical objects beyond our Solar System for more than 200 years. It contains 110 star clusters, nebulae, and galaxies, among them most of the brightest and finest deep sky highlights that are visible from northern skies. Amateur and professional astronomers alike have turned their telescopes time and again to the Messier objects. Numerous books have covered them, and numerous websites attest to their unwavering popularity. However, a current overall picture of the catalog and its objects was missing, as much information currently disseminated is actually outdated. So, for the first time since Robert Burnham’s famous Celestial Handbook, a thoroughly investigated new account with historical, astrophysical, and observational information on all the objects had to be conducted. Many discrete tasks were associated with this book. Historical information on Charles Messier, his observations and his catalog had to be compared to latest level of knowledge. In addition to our own research, the biography published by Jean-Paul Philbert in the French language proved especially helpful. The main task was the compilation of recent astrophysical information on all of the objects. More than 500 scientific papers were compiled and evaluated. These texts are complemented by extensive observational notes, which incorporate the visual use of large modern reflectors. A major part of the book is the more than 150 fantastic photos by leading amateur astrophotographers from all over the world. Occasionally, these images are accompanied by photographs from the Hubble Space Telescope, where this adds value. In addition, an extensive collection of visual drawings is shown, both from the classical era of the nineteenth century, as well as modern sketches drawn by the author himself. The compilation of this book took much effort over the past five years. Many of the images were prepared exclusively from such exotic
spots as Greece, Chile, and Namibia. They combine more than 5000 minutes of photographical exposure and 150 hours of visual observation. From the original German edition, which was released in 2006, information and photos have been updated and improved. I owe a very personal thank you to the co-authors of this book. Stefan Binnewies, the well-known German astrophotographer, conducted the orchestra of his colleagues. Susanne Friedrich, professional astronomer and amateur alike, ensured the quality of the astrophysical information. Finally, Prof. Klaus-Peter Schroeder, also a professional astronomer, who has worked in the United Kingdom and the United States for decades, translated and updated the texts. A deeply felt thank you goes to the astrophotographers who contributed so much to this book, especially to the teams of Volker Wendel and Bernd Flach-Wilken, Josef Pöpsel and Dietmar Böcker, and Robert Gendler and Jim Misti. I would also like to thank Lutz Clausnitzer, Klaus Wenzel, Arndt Latusseck, Wolfgang Steinicke and Matthias Juchert, who helped in many respects on the German edition. The fact that this book appears in an English language edition is almost a miracle. Among the many people who have helped that this dream became reality are Owen Brazell, David Eicher, Phil Harrington, Yann Pothier, and Stewart Moore. Additionally, I am greatly indebted to Sue French, who proofread the manuscripts and supported this project to a very great extent, and David Levy, who authored the foreword in his unparalleled manner. Finally, I would like to thank Vince Higgs and the team at Cambridge University Press for their support, work, and faith. May this book give you new insights into your favorite deep sky highlights.
Erlangen, Germany Ronald Stoyan
9
User guide The data files Degree of difficulty: rating of the observational difficulty: 1 object easily visible to the naked eye 2 object difficult to see with the naked eye 3 object easily visible in 8×30 binoculars 4 object easily visible in 10×50 binoculars 5 object difficult to see with 10×50 binoculars For more information about visual and photographic difficulty, see page 63. Minimum Aperture: minimum aperture required to see the object under a dark mountain sky, according to the personal experience of the first author. There are four categories: • naked eye • 15mm • 30mm • 50mm Designation: catalog number in the NGC (New General Catalogue) or the IC (Index Catalogue). Type: Object type. For a more detailed introduction to the different types, see page 53. Class: Classification of the object, specific to its type: • Galactic nebulae: distinction between emission nebula and reflection nebula, see page 53 • Open clusters: Trümpler classification, see page 55 • Globular clusters: concentration class, see page 56 • Galaxies: Hubble classification scheme, see page 61
• galaxies: H2000 (multiple authors: “The Hubble Space Telescope Key Project on the Extragalactic Distance Scale,” Astrophysical Journal 529, 698, 745, 786 (2000) • Virgo cluster galaxies: V2004 (Sanchis, T., et al.: “The origin of HI-deficiency in galaxies on the outskirts of the Virgo cluster. II. Companions and uncertainties in distances and deficiencies,” Astronomy and Astrophysics 418, 393 (2004) • Virgo cluster galaxies: V2002 (Solanes, J.M., et al.: “The Threedimensional Structure of the Virgo Cluster Region from TullyFisher and HI data,” Astronomical Journal 124, 2440 (2002) • extragalactic HII regions: HK83 (Hodge, P.W., Kennicutt, R.C., Jr.: “An atlas of HII regions in 125 galaxies,” Astronomical Journal 88, pp. 296 (1983) In addition, alternative results have been quoted, in order to demonstrate the uncertainty of the distances given. If available, the distance measurement method is indicated. Size: physical diameter of the object, as calculated from its actual distance and angular diameter. The resulting values may differ from the ones stated by original sources. Spiral galaxies seen under some inclination may be underestimated. Constellation: Latin name of the constellation in which the object is located R.A.: Ascension for the equinox 2000.0 Decl.: Declination for the equinox 2000.0 Magnitude: apparent total visual brightness
Distance: Distance from Earth in light-years. As far as possible, uniform sources have been used, i.e.: • galactic nebulae and open clusters: K2005 (Kharchenko, N.V., et al.: “Astrophysical parameters of galactic open clusters,” Astronomy and Astrophysics 438, 1163 (2005) • globular clusters: Rww2005 (Recio-Blanco, A., et al.: “Distance of 72 galactic globular clusters,” Astronomy and Astrophysics 432, 851 (2005)
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Surface brightness: mean visual brightness in magnitudes per square arcsecond (not given for star clusters) Apparent diameter: apparent (angular) photographic diameter
The texts History
Observation
The historical sections include translations from the original quotations of historic observers from the seventeenth to the early twentieth century. In part, these have been translated from the original. Where not available, they had to be taken as quotes from secondary literature. English quotations are given, as far as available, in their original wording. Frequently, the term “resolution” (of an object) is used in historic texts – not just for star clusters, but for galaxies and nebulae as well. In the nineteenth century, that did not necessarily mean the resolution into individual stars, as we use the term today, but rather resolution of any kind of detail. A short introduction to every historic observer quoted in this book can be found on page 28.
The information and advice given for the visual observation of each object is based on the personal experience and observation of the first author, using telescopes of different apertures. Each object has been observed on several occasions, some more than a dozen times. The instrumentation used consisted of: • 3.5×15 opera glass, “Theatis” made by Carl Zeiss Jena • 8×30 binoculars, “Deltrintem” made by Zeiss Jena • 10×50 binoculars, “Dekarem” made by Carl Zeiss Jena • 20×100 binoculars, made by Miyauchi • 120/1020mm (4.7-inch) refractor “Star 12ED,” made by Astro-Physics, magnifications from 25× to 255×, in exceptional cases 340× and more • 360/1780mm (14-inch) Newtonian on a Dobsonian mount, magnifications from 45× to 593×, entirely manual operation, observing sites in the German countryside (Kreben, naked-eye limiting magnitude 6.5, sky surface brightness 21.0 mag/arcsecond2) and Austrian Alps (Tiefenbachferner, naked-eye limiting magnitude 7.0 mag, sky surface brightness 21.6 mag/arcsecond2) • 500/2500mm (20-inch) Newtonian on a Dobsonian mount, magnifications from 63× to 625×, Farm Tivoli, Namibia (naked-eye limiting magnitude 7.5, sky surface brightness 21.8 mag/arcsecond2)
Astrophysics Ever since the publication of the famous “Burnham’s Celestial Handbook” in the 1970s, amateur astronomers have been waiting for a new, up-to-date compilation of astrophysical data on all Messier objects. A lot of literature, internet sources in particular, refers to outdated values. For this book, the content of over 500 professional, up-to-date publications was researched. This was made possible by the use of the Internet and the free NASA service known as the Astrophysical Data System (ADS), which is an on-line collection of almost all scientific publications in astronomy. The exact citations are given in the Appendix. Where possible, no sources older than 10 years were used, but a few objects have received little attention in modern references. Other objects (M 1, M 31, M 42) catch a lot of professional attention, and the vast amount of literature dealing with them would easily permit a much more detailed treatment. However, space restrictions limited this book to the most relevant information. In many cases, the research presents surprises: modern scientific results often disagree completely with what is commonly believed as the result of outdated literature. This trend will continue, as there is a steady stream of new observations and their astrophysical interpretation. Hence, the statements made in this book must be regarded as only a momentary picture of our knowledge from the years before 2007. Many questions remain unanswered, and we expect new insight into topics such as dark matter, black holes or the age of the Universe. This may affect how some aspects of the Messier objects will be explained in the future. Another common problem is the disagreement of modern sources from one another. Different authors have different opinions, and different methods yield different results. Generally accepted knowledge grows out of long debate and testing. This is part of the lively nature of a quickly developing science such as modern astrophysics.
Observing comments refer to a very experienced observer and excellent observing sites with a dark, moonless sky. We have purposely omitted star charts and all advice on finding the objects, since there is already a vast literature on these aspects, useful even to the first-time observer. However, we recommend a versatile software-based approach, “Eye & Telescope.” It produces star charts and visibility information based on actual sky conditions and the instrument used.
11
The pictures Selected images showcase the fantastic results of the amateur astrophotographer’s community. To document astrophysical aspects beyond the reach of amateur photos, we have complemented the material with NASA pictures of many Messier objects, obtained by the Hubble Space Telescope (HST). Some Messier objects are particularly popular with amateurs, and good images are abundant. Others grab almost no attention and only a few pictures of lower quality are available. It’s virtually impossible to get photos of uniform quality for all 110 objects. For this reason, the scale and depth (i.e., limiting magnitude) of the photos vary from object to object. The photos printed in this book were taken in the years between 1995 and 2007. The most common technique is tri-color (red, green, blue) photography with a cooled CCD camera and (L)RGB filter wheel. With a few exceptions, traditional film-based photography can no longer compete, while the new era of digital cameras and DSLRs is just about to begin. For accurate technical information on each picture, refer to the picture credits in the appendix section. The color reproduction is neither uniform, nor should it be regarded as quantitatively correct. Color-balance and saturation depend on a number of factors, such as chip-characteristics, filter-transmission, software and personal judgment during image processing. The result is often subjective, perhaps aimed at reproducing the colors of professio-
nal photos. After all, techniques of absolute color calibration are timeconsuming and do not apply to some types of astronomical objects, most notably the emission nebulae. The techniques used by amateur astronomers for their image-processing work differ a lot from person to person, and there are no general standards. Some photographers would remove traces of planetoids, satellites or ghost-images by hand, on a pixel-to-pixel basis, others accept them as part of the authentic picture. Composite images made from several different exposures change the perception of the intensity range. This technique is used to accommodate large intensity variations and to avoid “burnt-out” central regions. But it may make stars on bright nebulous background appear significantly less brilliant than they are in reality. A good example is the Trapezium in the Orion Nebula. Hence, a quantitative interpretation of such a photo is impossible, but amateur astrophotographers are happy to accept that, in order to produce the most appealing image of an object. Together with the photographs, historical and modern drawings have been reproduced here. The manual sketch of an object as perceived through the telescope eyepiece was the only scientific method of recording until the late nineteenth century, after which photography finally took over. This book shows a large number of fine sketches from the pre-photographic era. Differentiating real physical changes in the objects from artistically diverse sketching styles and personal
A photo in the works: M 42. At left is a single image taken with the green filter, in the middle a raw tri-color image, at right the fully processed LRGB composite.
12
perceptions had been a continual problem. Today, amateurs keep the tradition of astronomical drawings alive, in order to sketch their visual impression of a specific object. Drawings are subjective and contain erroneous perceptions. Nevertheless, this method is an independent recording technique, complementary to the capabilities of photography. Before criticizing historical drawings for their misconceptions, we should keep in mind that it is always easier to verify a known feature than to discover it. In that sense, the historic drawings must be regarded as more “honest” than their modern counterparts. Even the most critical modern observer cannot avoid the subconscious knowledge of an object by modern photography and its influence on his or her perception of it. Drawings differ from photographs in a number of ways. For one, the eye can not accumulate light over a long time, as a photographic emulsion or chip can. Furthermore, the visual response to a large brightness range is much more logarithmic than the photographic response. And finally, the spectral response of the eye also differs from that of photographic emulsions or chips. With emission nebulae, in particular, visual and photographic views emphasize different features. The author’s drawings were specifically made for this book. The objects were observed several times with different apertures. Frequently, several attempts were required before an acceptable result was achieved. All the sketches are of a cumulative nature: each drawing summarizes the visual impressions of an object collected over many hours or even nights under a dark sky in the countryside, in the mountains or in the Namibian desert. The results are not to be confused with a quick sketch made by the eyepiece! The observing time involved was at least an hour, as for a simple elliptical galaxy, and up to three nights for large objects with a lot of detail. The original sketches are drawn with pencil, black on white. So are the proper drawings, using in addition an eraser and a smudging tool. For an inversion to white on black, the drawing is scanned and the tonal range adjusted, but no further digital manipulations are made. Subtle contrasts are over-pronounced by the drawings, as they would otherwise be lost in print.
A drawing in its work-stages: M 42. Above is the original pencil sketch, below the properly redrawn and then inverted result.
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14
Charles Messier
1730 to 1751: Childhood and adolescence Charles Messier was born on the 26th of June 1730 in Badonviller, as the tenth child of the court bailiff Nicolas Messier (1682–1741) and his wife Françoise (maiden name Grandblaise, deceased 1765). His home village lies near the former German–French language border in the western part of the Vosges Mountains in Lorraine. In Messier’s days, that region did not belong to France but to the independent dukedom of Salm. The Messier family was one of the richest in the little state, with high-ranking positions and excellent connections, which would later be very helpful to the young Charles. He grew up in a house opposite the evangelic church of Badonviller, by a square which today bears his name. Six of his siblings died in their early childhood. An important role in Charles’ life was played by his eldest brother Hyacinthe, who was older by 13 years. Hyacinthe started his professional career as an auctioneer and, eventually, became the highest financial officer of the dukedom. When their father died in 1741 – Charles was only 11 years old then – Hyacinthe was already able to take care of the Messier family. He gave Charles an apprenticeship in his office, mostly involving paper work. That helped develop the boy’s good writing and drawing skills, and the accuracy required for finance and business. His first interest in astronomy was sparked by the large, six-tailed comet of 1744, discovered by the Swiss de Chéseaux, and the annular solar eclipse of 1748. The year 1751 brought important changes to the life of the Messiers. The dukedom of Salm lost its independence by becoming part of Lorraine, which later fell to France by annexation. Only the former residence of the dukes of Salm, the village Senones, a few kilometers from Badonviller, retained its independence and was to become the new home of the Messier family. Now at the age of 21, it was time for Charles to seek a life of his own. With the help of a good family friend, who had contacts in important circles in Paris, an assistantship at the new Naval Observatory in Paris became available to Charles Messier. It was not really his interest in astronomy which got him the offer, but his good skills as an office assistant. He left Badonviller on the 23rd of September 1751.
Charles Messier at the age of 40, painted by Ansiaume. Messier commented that his portrait was most appropriate but made him look younger than he really was.
15
1751 to 1757: Assistant of the Naval Observatory
Drawing of the Hôtel de Cluny, from the beginning of the nineteenth century. The octagonal sheltered platform of the tower is Messier’s observatory.
Today, the Hôtel de Cluny is one of the most beautiful medieval buildings of central Paris. It hosts the National Medieval Museum, but there is no commemoration of the work of Charles Messier.
16
Joseph-Nicolas Delisle (1688–1768), who taught mathematics and astronomy at the Collège Royal in Paris (later to be the Collège de France), built a private observatory on the stairtower of the Hôtel de Cluny in 1747, opposite to the Collège Royal. Originally, the Hôtel de Cluny was the Parisian residence of the Benedictine monks from the great abbey in Burgundy. Later, it became the property of the French Navy. In 1754, the aged Delisle made a deal: he signed over the observatory to the Navy and in return, he received the custom-tailored title “Astronomer of the Navy.” Delisle’s humble observatory stood in the shadow of the established Royal Observatory of Paris, which was well known as a leading European institution for astronomers like Huygens, Cassini, and Maraldi. Delisle, by contrast, was not part of the French astronomy establishment. Hence, Messier entered a professional environment which allowed him to pursue his astronomical interests without any scientific obligations, but which also branded him from the outset as an outsider to professional astronomy. The childless Delisle couple received and hosted Messier as though he were their own son, and he lived with them in their apartment in the Collège. Delisle’s assistant Libour introduced Messier to the basics of astronomy, and the young Messier’s first tasks were to make hand-drawn copies of maps and to write the observing logs. Delisle had been in personal contact with the late, famous English scientists Newton and Halley. The latter had pointed out in his famous work of 1705 that the comet apparitions of 1456, 1531, 1607, and 1682 were due to the same physical comet, which would reappear in 1758. Delisle made an independent calculation of the comet’s orbit and derived April 1759 for the perihelion passage. Based on his master’s work, Messier drew a map of the comet’s path among the stars and had orders to watch for it from the summer of 1758 onward. That comet hunt was the first real astronomical task given to the 28-yearold, who so far had carried out only basic observations. Messier understood that this was the chance of a lifetime; he wanted to be the first to prove Halley’s milestone work. But life took a different course. While Messier did rediscover the comet on the 21st of January 1759, he soon had to learn that a farmer in Saxony had beaten him by about a month: the previously unknown amateur astronomer Johann Georg Palitzsch (1723–1788) from Prohlis near Dresden had already spotted Halley’s Comet on Christmas night 1758. Messier had confined his search to Delisle’s orbital path for too long. And to his great dismay, Messier could not even get his master’s permission to publish his independent discovery, since Delisle did not believe that he’d made a mistake in his calculations. He thought the comet was an unrelated object. Messier bowed to the wishes of his master and host and withheld his obser-
1
2 City map of Paris from the year 1771. The Hôtel de Cluny (1) and the Royal Observatory of Paris (2) are circled.
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Custos Messium – a constellation for the comet hunter In 1775, the first version of the now enormously popular Messier catalog of 110 nebulae had been out for one year, with then only 45 objects. However it was his achievements as a recordbreaking comet discoverer that made Charles Messier the publicly bestknown astronomer of his country. In fact, Messier had discovered practically all the comets of the past 15 years. He had been a member of the elite circle of the French Academy of Sciences since 1770. But now, a very special honor was awarded to him, unprecedented in the history of astronomy. Jerôme de Lalande (1732-1807), a famous author, professor and colleague of Messier, created a new constellation on his freshly published stellar globe: “Custos Messium” (lat.), the “Harvest Guardian.” Concerning his motives, Lalande wrote: “This name will remind future astronomers of the courage and diligence of our industrious observer Messier, who since 1757 appears occupied with the sole task of patrolling the sky to discover comets.” Contemporary French star charts happily included the new constellation under its French name “Messier,” picturing a guardian who watched over a cornfield. The “Harvest Guardian” had its place north of Cepheus, Cassiopeia, and Camelopardalis. Today, its space has become part of these three constellations. Messier’s constellation held only one noticeable star, 40 Cas, and no remarkable deep-sky objects. As Messier related, Lalande chose that particular part of the sky, because it once hosted the comet of 1774, discovered by Montaigne. It was the only one of 14 comets that, following the death of his wife, Messier failed to discover himself. These were two big losses, which Messier could not bear – and Lalande must have been aware of that. Lalande created two other new constellations: “Felis,” the cat (between Hydra and Antlia), in memory of his favorite pet, and “Globus Aerostaticus” (between Capricornus
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The constellation Custos Messium (Harvest Guardian), pictured in Johann Elert Bode’s “Vorstellung der Gestirne” (1782).
and Piscis Austrinus) to commemorate the invention of the hot-air balloon by the brothers Montgolfier and their first air-borne voyage in 1799. All three constellations were included in J.E. Bode’s Prussian star atlases – despite, certainly, some national rivalry. But in return, Lalande would include in his atlases the “Brandenburg Scepter,” “Frederick’s Honor,” and the “Mural Quadrant,” which Bode had invented. Nevertheless, all these new constellations fell out of use only 80 years later.
Joseph Jérôme le Français de Lalande, colleague and friend of Messier. Engraving by André Pujos.
vations for three months, until it was finally clear that Delisle was wrong. However, the long-delayed publication aroused suspicion and skepticism among the royal astronomers in Paris. His independent discovery was not acknowledged – a disappointment that Messier would not forget for a long time. In hindsight, we know that the by-products of Messier’s diligent comet hunt were much more rewarding. In August 1758, when he was observing the comet discovered by de la Nux, Messier came across a yet unknown nebula which looked exactly like the comet. This discovery sparked the idea for his catalog, which retains Messier’s name to this day. Hence, Messier made good use of that chance of a lifetime, after all – albeit in quite a different way than he, the comet enthusiast, had anticipated.
Johann Georg Palitzsch succeeded in what Messier tried in vain: he was the first to rediscover Halley’s comet on its return in 1758.
1759 to 1770: Comet discoveries and recognition Comet hunting became an obsession for Charles Messier. Between 1758 and 1804, he spent more than 1100 nights on this task. He became the first real “comet hunter" in history, with a prototypical character: a most diligent observer with humble equipment but much enthusiasm, who would search for new comets with systematic endurance. He observed 44 comets altogether, more than were known to science before him. He discovered 21 comets, 6 of which are regarded today as codiscoveries. Messier was, in fact, the first observer who systematically used the telescope for comet hunting. Before him, comets were usually discovered with the naked eye. But he did not leave it with the discovery of a comet. He would observe every comet for as much and as long as possible; his record was 71 nights over a period of 6 months. Furthermore, Messier measured comet positions to make orbit calculations possible. He never did that himself, though, as he was entirely devoted to observation. None of his many publications would contain a single bit of math or theoretical work. In that respect, Messier’s close friendship with Jean Baptiste Gaspard Borchart de Saron (1730–1794) was most beneficial. Saron came
Joseph Nicolas Delisle, teacher and benefactor of Messier. Engraving by Konrad Westermayr.
from an established, noble family and was soon to become the royal state-attorney, and later even president of the parliament. Theoretical astronomy was one of his hobbies – a perfect match: Saron’s quick calculations were essential to Messier’s success, because these allowed him to find a comet again, even after a long period of bad weather. For the discovery of the great comet of 1760, Messier was still a day late. But only a few days later, on the 26th of January 1760, he discovered the first comet named after him. In the following years, Messier nearly achieved a monopoly on comet discoveries: all eight known comets between 1763 and 1771 were discovered by him! Messier was active in other respects, too. Between 1752 and 1770, he observed 93 lunar occultations and 400 eclipses of Jupiter’s satellites, he watched 5 solar eclipses, 9 lunar eclipses, and he measured 400 stellar positions. Over the course of his lifetime, Messier followed four Mercury and two Venus transits, and he did a lot of planetary observing, especially on Saturn. In 1767, he made a three-month-long sea cruise to test astronomical clocks on the coasts of the Netherlands and Belgium. Recognition by the international science community was soon to follow. In 1764, he became elected a fellow of the English and Dutch scientific academies. Such academies were of crucial importance in the eighteenth century. Only their membership made it possible to exchange correspondence with the leading scientists of the time and gave access to the accumulated knowledge of their libraries. Messier had to wait a long time for admission to the French academy of the sciences – in Paris, the skepticism aroused by his long withheld observations of Halley’s comet were still not forgotten. But, at least, his salary was raised in 1765, after the retirement of Delisle from active research. Messier’s breakthrough with the French astronomy establishment came with his discovery of the great comet of the year 1769. That comet was a spectacular sight, and it made its discoverer’s name so popular with the general public that the king would personally receive a map drawn for him by Messier. The king nicknamed Messier “the comet nest-robber,” because for many years not a single comet “slipped out of its egg” that hadn’t already been discovered by Messier. This idea then developed into the popular nickname “the comet-ferret.”
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The role-model: Nicolas-Louis de Lacaille Nicolas-Louis de Lacaille (1713–1762) was born on the 15th of May 1713 in Rumingy near Reims. As a son of noble parents, he began to study theology in Paris. He was 26 when he made his first recorded astronomical observations. Soon, he became professor at the Collège Mazarin in Paris, where in 1746 he constructed an observatory, and finally in 1741 he was admitted to the French Academy of Sciences, with the support of the Duke of Bourbon. Lacaille was well known for his accurate observations and an overeagerness to work – in fact, he died of overwork on March 21st, 1762. Hence, in 1751, the French academy chose him for a longer stay at the Cape of Good Hope, in order to accurately measure geographic longitudes and the positions of southern stars. Meanwhile, his scholar Lalande was his counterpart in Berlin for a program of simultaneous observations, which led to improved distance measurements of the planets and the Moon. Lacaille arrived in South Africa in April 1751. At the foot of Table Mountain, which he honored with the constellation “Mensa,” he began the observations for a southern star catalog in August 1751. For that work, Lacaille used a mural quadrant, equipped with a very small telescope of only ½-inch (12.5mm) aperture Abbé Nicolas-Louis de Lacaille, and a magnification of 8×. painted by Melle Le Jeuneux, A year later, in July 1752, 1762 this catalog contained the positions of 9776 stars. While cataloging the heavens, Lacaille made a list of the nebulous objects he came across, which he published in 1755. It was the first of its kind, and it is appended to Messier’s third and final catalog. Thirteen new southern constellations were created by Lacaille as a by-product of his work: Antlia, Caelum, Circinus, Fornax, Horologium, Mensa, Microscopium, Norma, Octans, Pictor, Reticulum, Sculptor, and Telescopium. With these, Lacaille filled in the coarser pattern of southern constellations created 150 years earlier by Keyzer. In addition, Lacaille changed the name of the constellation Abies into Musca – not to be confused with a lost northern constellation of that name – and he suggested splitting the huge constellation Argo Navis into Carina, Vela, Pyxis, and Puppis. About 100 years later, these suggestions became widely accepted as astronomical conventions.
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The next year (1770), Messier discovered a comet, which was identified by the Swedish observer Lexell as a periodic comet. Two weeks after that discovery, Messier was finally admitted to the French Academy of Sciences, followed by membership in nearly all of the remaining foreign scientific associations. In addition, he received another pay rise and, in 1771, he inherited the title invented for Delisle, “Astronomer of the Navy.”
1770 to 1789: Changing private fortunes and observational successes On the 26th of November 1779, Messier married the daughter of a noble professor, Marie-Madeleine Dordolot de Vermauchampt, who was three years his junior. For 15 years, they had lived under the same roof in the Collége Royal. But in the absolutistic France of that time, a marriage between a bourgeois and a noble lady would have been impossible. Only the recent great success of Charles Messier changed their fortunes. In 1771, they moved into an apartment of their own in the Hôtel de Cluny – it was then only a few steps from Charles’ bedroom to the observatory. 1771 must have been one of the best years in Messier’s life. Besides his personal good fortune, he discovered two comets and completed the first version of his catalog, then totalling 45 nebulous objects, although Messier considered the latter a mere by-product of his searches, as he just wanted to avoid confusion when he was comet-hunting. On the 15th of March 1772, there was another reason for Messier to rejoice: his wife gave birth to a son, Antoine-Charles. But then his fortunes changed dramatically: a week later, Marie-Madeleine Messier died of puerperal fever, and the little baby followed her on the 26th of March. Messier’s reaction to this heavy double-blow to his private life is difficult to assess. The fact is, however, that he started a four-day observing campaign on comet Montaigne – the first comet in almost 10 years which had not been discovered by him – the very night his son died. In August 1772, Messier travelled to the dukedom of Salm, which in his own words he regarded as his “Fatherland.” He stayed some time with his eldest brother in Senones, following earlier visits in the years 1758, 1762, and 1770. Not surprisingly, Messier continued an intense observing schedule during that family visit. On his return to Paris, he was accompanied by his nephew Joseph-Hyacinthe and by his sister Barbe, who would take care of her brother until her death in 1797. The following years were characterized by continued comet observations. In 1780, Messier published the second version of his catalog, which contained 68 nebulous objects. The first new objects were found soon after his original catalog was printed. But Messier did not keep looking systematically for new objects, he just recorded accidental findings during his comet observations. Nevertheless, the third version of his catalog, with 103 objects, came out in 1781. This was mostly due to the wealth of input from his new colleague Pierre Méchain (1744–1804). Despite more such discoveries by Méchain after 1781, there were no further catalog versions.
Table: 44 comets, observed by Charles Messier Popular name
Old designation
Messier’s first observation
Messier’s last observation
Number of nights observed
Date of discovery
Discoverer
Aug 14,1758
Nov 2,1758
31
May 26, 1758
de la Nux
P/Halley
1759I
Jan 21, 1759
May 1, 1759
47
Dec 25, 1758
Palitzsch
Great Comet
1759III
Jan 8, 1760
Jan 30, 1760
6
Jan 7, 1760
Chevalier
Messier
1759II
Jan 26, 1760
Mar 18, 1760
22
Jan 26, 1760
Messier
May 28, 1762
Jul 5, 1762
20
May 17, 1762
Klinkenberg
Messier
1763
Sep 28, 1763
Nov 24, 1763
29
Sep 28, 1763
Messier
Messier
1764
Jan 3, 1764
Feb 11, 1764
16
Jan 3, 1764
Messier
Messier
1766I
Mar 8, 1766
Mar 15, 1766
8
Mar 8, 1766
Messier
P/Helfenzrieder
1766II
Apr 8, 1766
Apr 12, 1766
5
Apr 8, 1766
Helfenzrieder
Messier
1769
Aug 8, 1769
Dec 1, 1769
42
Aug 8, 1769
Messier
P/Lexell
1770I
Jun 14, 1770
Oct 3, 1760
47
Jun 14, 1770
Messier
Great Comet
1770II
Jan 10, 1771
Jan 20, 1771
4
Jan 10, 1771
Messier
Messier
1771
Apr 1, 1771
Jun 15, 1771
48
Apr 1, 1771
Messier
Mar 26, 1772
Apr 3, 1772
4
Apr 8, 1772
Montaigne
Messier
1773
Oct 12, 1773
Apr 14, 1774
71
Oct 12, 1773
Messier
Aug 18, 1774
Oct 25, 1774
41
Aug 11, 1774
Montaigne
63
Jan 6, 1779
Bode
Bode
1779
Jan 19, 1779
May 19, 1779
Messier
1780I
Oct 27, 1780
Nov 28, 1780
13
Oct 27, 1780
Messier
Méchain
1781I
Jun 30, 1781
Jul 16, 1781
14
Jun 28, 1781
Méchain
Méchain
1781II
Oct10, 1781
Nov 5, 1781
12
Oct 9, 1781
Méchain
Nov 27, 1783
Dec 21, 1783
13
Nov 19, 1783
Pigott
Feb 3, 1784
May 25, 1784
13
Jan 24, 1784
Cassini
Messier
1785I
Jan 7, 1785
Jan 16, 1785
6
Jan 7, 1785
Messier
Méchain
1785II
Mar 13, 1785
Apr 16, 1785
14
Mar 11, 1785
Méchain
P/Encke
1786I
1
Jan 17, 1786
Aug 1, 1786
Oct 26, 1786
43
Apr 11, 1787
May 20, 1787
6
Nov 25, 1788
Dec 29, 1788
20
Nov 25, 1788
Messier
Jan 3, 1789
Jan 6, 1789
2
Dec 21, 1788
C. Herschel
1
Jan 7, 1790
C. Herschel
Méchain
1787
Messier
1788I
Jan 19, 1786
Jan 19, 1790 P/Tuttle
Messier
Messier
1790II
1793I
1798I
Méchain C. Herschel
Apr 10, 1787
Méchain
Jan 10, 1790
?
7
Jan 9, 1790
Méchain
May 1, 1790
Jun 9, 1790
45
Apr 17, 1790
C. Herschel
Dec 26, 1791
Jan 28, 1792
12
Dec 15, 1791
C. Herschel
Feb 1, 1793
Feb 14, 1793
6
Jan 10, 1793
Gregory, Méchain
Sep 27, 1793
Dec 8, 1793
25
Sep 24, 1793
Perny
Sep 27, 1793
Messier
Aug 14, 1797
Bouvard
Sep 27, 1793
Jan 7, 1794
Aug 16, 1797
Aug 30, 1797
13
Apr 12, 1798
May 24, 1798
27
Apr 12, 1798
Messier
Dec 7, 1798
Dec 12, 1798
4
Dec 6, 1798
Bouvard
Méchain
1799I
Aug 10, 1799
Oct 25, 1799
44
Aug 7, 1799
Méchain
Méchain
1799II
Dec 28, 1799
Jan 6, 1800
5
Dec 26, 1799
Méchain
Pons
1801
Jul 12,1801
Jul 21, 1801
5
Jul 12, 1801
Pons, Messier, Méchain, Bouvard
Aug 30, 1802
Sep 5, 1802
7
Aug 26. 1802
Pons
Mar 11, 1804
Mar 17, 1804
6
Mar 7. 3. 1804
Pons
adopted from: Philbert, J.P.: Charles Messier – le furet des comètes
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The competitor: Johann Elert Bode Messier not only reinvented comet hunting, he blication of Messier’s first catalog of 45 nebulae, also sparked new interest with his contemporariBode started his own search for new nebulae and es in the observation of nebulae and star clustar clusters. He succeeded with some genuine sters. The German astronomer Johann Elert Bode discoveries (M 81, M 82, M 53, M 92) and a larger (1747–1826), who like Messier published an number of independent findings. In 1777, he comannual almanac, entered into a direct competitipiled his “Complete Catalog of all Observed Nebuon with the French astronomer in 1777, by prelae and Star Clusters,” based on his own observasenting his own catalog of nebulous objects. tions as well as on all references he could find in Bode developed an interest in astronomy at a the literature. At its time the largest deep-sky cayoung age. He observed the night sky from a talog, this included 75 objects. Bode continued to hatch in the roof of his parents’ house in Hamobserve, and he always encouraged other obserburg. By chance, a math professor saw Bode’s vers to publish their data in his almanac. The 1779 notes and encouraged him volume contains a listing of to write a popular astronoobjects found by Köhler from my book. In 1768 at just 21 Dresden, and other editions years old, Bode published reproduced the notes of the guidebook “Deutliche Oriani and a translation of Anleitung zur Kenntnis des Messier’s catalog. gestirnten Himmels” (“ConAn updated and enlarged list cise manual to the knowof contemporary observaledge of the starry sky”), tions of nebulae, still wiwhich was received very thout knowledge of Messier’s well and reprinted several third catalog version but times. A later edition was including the 68 objects of used to publish the formula his second, was published for the distances of the plaby Bode in 1782 within the nets, which was soon known “Vorstellung der Gestirne.” as the “Titius-Bode-Law.” This list not only included Still an amateur astronomer, several new discoveries, preBode observed the Venus sumably made by Bode himtransit of 1769. But in 1772, self, but also the objects IC he began to work at the Johann Elert Bode 4665 (already mentioned by royal observatory of Berlin, Al Sufi) and h & F Persei. and a few years later, in Despite the substantial work 1779, Bode discovered his first comet. Much like of Bode in this field, his name is hardly known Messier, that discovery gave him recognition. He today, by contrast to popular Messier. One good eventually became the director of Berlin Obserreason may be that Bode did not check the posivatory in 1787 and kept that office for 38 years. tions of objects contributed from other observers. Bode gained some fame as the founder of the That caused many errors in his list. His listing of “Berliner Astronomisches Jahrbuch” (“Berlin Astro- 1782, for example, contains three different entries nomical Almanac”) and with his book “Vorstellung for M 8, because Bode did not realize that the difder Gestirne” (“Introduction to the Constellations,” ferent positions from Messier, Le Gentil, and Köh1782) and the monumental celestial atlas “Uraler all referred to the same object. Hence, despite nographia” (1801). By contrast to Messier, Bode Bode’s strive for completeness, Messier’s final cawas well connected in scientific circles. The name talog of 1781 was, at its time, second to none in “Uranus” for the new planet discovered by William terms of quality. Herschel was his suggestion. And as director of the Berlin Observatory, he had excellent contacts all over Europe. In 1774, three years after the pu-
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The 13th of March in that same year saw the discovery of the planet Uranus by William Herschel in England. At first, Herschel took his new object for a possible comet and asked Charles Messier for his opinion. The same day he received Herschel’s letter, Messier observed Uranus. Messier passed his positional measurements down to de Saron to calculate the orbit. His mathematical friend was quick to realize that Uranus was not a comet but a new planet. After 1781, Herschel would find over 2000 new nebulous objects with his much better telescopes. However it was not only this superior competition that stopped Messier working on nebulae, but also another blow of fate: on the 6th of November 1781, Messier was on a walk with his family in the Park Monceaux. His curiosity led him to inspect the entrance to a basement, when he slipped and fell 8 m (24 feet) into a deep ice-storage cellar. Messier was seriously injured, and had broken his upper leg, upper arm, two ribs and the wrist of his hand. He lost a lot of blood from an open wound over his eye. It took him the better part of 1782 to recover from this bad accident. His leg had to be broken again, after the bones had healed at an angle. Messier was bed-bound for a long time, and he always limped thereafter. Herschel, who paid him a personal visit in Paris 20 years later, remarked that Messier never fully recovered from that injury. It was a full year after that accident before Messier was back in his observatory, on the occasion of the Mercury transit of the 12th of November 1782.
1789 to 1804: In the turmoil of the French Revolution The French Revolution began with the storming of the Bastille in Paris on the 14th of July 1789. As for so many, the following years brought chaos and insecurity to Messier. The structures of the French Navy were dissolved
and maintenance of the observatory ceased. Frequently, Messier had to borrow oil for his observing lamp from his good colleague Lalande. The latter was now director of the former Royal Observatory of Paris, and they knew each other well from the days when they both taught at the Collège Royal. In 1793, by decree of the revolutionary directorate, all academies were dissolved, with serious consequences for Messier. A further tragic event for Messier was to follow on the 20th of April 1794 when his good friend and benefactor de Saron was guillotined under the reign of terror. Already in prison, he calculated his last comet orbit for Messier. Fundamental changes were also imposed upon Lorraine. In 1793, the dukedom of Salm became part of revolutionized France by annexation, with significant consequences for the Messier family, which was closely involved with the local nobility. Some family members emigrated from France to Germany, following the dukes of Salm.
In 1795, a new astronomical institute was founded in Paris: the Bureau des Longitudes. Its original purpose was to outstrip the superiority of the English clocks. Messier was not among its founding members, like Méchain or Cassini, but he replaced the latter in the next year. In 1798, still living in the Hôtel de Cluny, Messier was on his own again, after the death of his sister in the previous year. From Senones, his younger brother and his niece Josephine now came to live with him. Josephine would take care of Charles Messier until his death. In 1801, Messier made his last comet discovery at the age of 71. Thereafter, he just lived off his past fame, which was finally recognized by the new regime. Napoleon personally bestowed him with the Cross of the Legion of Honour. This led Messier to make, in 1808, a connection between his discovery of the great comet of 1769 and the simultaneous birth of “the Napoleon the Great.” This idea was so close to astrology that it did not go over well with most contemporary astronomers.
The colleague: Pierre Méchain Thirty of the now so-called “Messier objects’’ were, in fact, discovered by Pierre Méchain (1744–1804). He was a close collaborator of Messier and helped complete his final catalog in the years 1779 to 1781. Pierre Méchain was born in Laon. He planned to become an architect, but lack of finances forced him to abandon his studies. Rumour has it that he even had to sell his telescope, which he had bought as an amateur astronomer, and that the buyer turned out to be Jérôme de Lalande, later (1794) to become the director of Paris observatory. Lalande had been astronomy professor at the Collège Royal from 1760 to 1767, as the successor of Delisle, and from 1794 to 1807 he was also editor-in-chief of the Connaissance des Temps. In 1772, he managed to get Méchain a job at the treasury of the French Navy in Versailles. Two years later, Méchain obtained the official position of a “calculator.” The connection with Messier’s friend Lalande initiated Méchain’s contribution to the Messier catalog. In 1781, Méchain found two new comets – eventually, his total score grew to eight discoveries. Unlike Messier, he was able to calculate his own orbits. His most famous discovery was the comet of 1786, which was proved by Encke’s orbital calculations to be the secondknown periodic comet (after Comet Halley).
From 1786 on, Méchain was engaged in longitude measurements. This work requires clocks much more accurate than those available at the time – a big problem for offshore navigation, as well as for geodesy on land. Hence, in 1791, the French Academy of Sciences started a project to define the French prime meridian from Dunkirk in the north to Barcelona in the south. After the project finished in 1795, Méchain found an error of 3" in the calculated latitude of Barcelona (about 90 meters on the ground). We know now that this was due to a combination of instrumental inaccuracies and some deviation of the globe from a perfect sphere – but Méchain expended considerable effort trying to further increase the Pierre Méchain, painted by Hurle. accuracy of the calculations. In 1798, he succeeded Lalande as director of the Observatory of Paris. In an, Méchain contracted yellow fever and died on the 20th of September 1804. 1804, during field work in Spain to revise the measurements along the French prime meridi-
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Portrait of the comet hunter from 1801, at the age of 71, drawn by Cless from Weimar. Messier was reasonably tall for his time, measuring 1.68m (5 feet 6 inches), a little chubby, and his hair turned white around the age of 60.
The last comet that Messier was able to observe was the great comet of 1807. Thereafter, he suffered from failing eyesight. After 1808, he could no longer read or write. In 1812, he became paralyzed on one side, and dropsy set in around 1815. Messier finally died on the 11th of April 1817 at the age of 87 years. Three days later, he was buried in the cemetery of Père Lachaise. The speech at Messier’s grave was given by Delambre, secretary of the reconstituted Royal Academy of Sciences. He commemorated the comet hunter with the words: “He did not write a single book, nor any treatise in general or in particular, but his observations will for a long time enrich the collection of the Academy. His famous colleague Lalande has created a constellation in his honor, the only one bearing the name of an astronomer. It will keep the memory of him alive, but his name will remain with science, independent of this honouring act of friendship: in terms of the catalog of comets, in which the name Messier has been recorded as often as honestly.”
William Herschel continued with Messier’s work. Painting by Contel, from an engraving.
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The Observations
Work on the catalog M 1 and M 2: Beginnings and motivation Charles Messier’s first encounter with a nebulous object occurred during his preparations for the return of Comet Halley. When he observed Comet de la Nux for that purpose in August 1758, he came across an object in Taurus, which looked very similar to the comet, but it did not move. It was the 28th of August 1758 when Messier discovered the Crab Nebula, now known as M 1. He obtained the position of this apparently new nebula two weeks later (12th of September ). Messier did not know then that M 1 had already been found by Charles Bevis in England in 1731, and so took his observation for a new discovery. That kindled an interest that would eventually lead to his famous catalog. As he described it in 1801: What made me produce this catalog was the nebula which I had seen in Taurus, September 12, 1758, while I was observing the comet of that year. The shape and brightness of that nebula reminded me so much of a comet, that I undertook to find more of its kind, to save astronomers from confusing these nebulae with comets. I continued to observe with telescopes suitable for the discovery of comets, which was the purpose I had in mind when producing this catalog. Messier did not start a systematic search straight away. However, it was two years before he found M 2, with a Gregorian reflector of 30-inch focal length and a power of 104×. Only later was he to learn, during a search for comet observations from other astronomers, that this object had already been discovered in 1746 by Jean-Dominique Maraldi (1709–1788). Again, Messier was not the original discoverer.
M 3 to M 40: Systematic search for nebulae In May 1764, Messier finally started systematic work on the catalog of nebulae. He began with the “nebulosae” in the lists and literature known to him, in particular those from Hevelius, Huygens, Derham, Halley, de Chéseaux (of which, apparently, he had only an incomplete knowledge), Lacaille, and Le Gentil. In addition, he discovered new objects of his own; some of these, like M 39 and M 40, while trying to verify entries from old catalogs. In only five months, Messier observed
and measured the positions of M 3 to M 40, including 19 genuine first discoveries. Hence, the first version of his catalog was more or less accomplished within half a year of work, from spring to fall 1764. That time must be considered the most productive phase in the life of Charles Messier as a “deep-sky observer,” as we would put it today, and it laid the foundation for his lasting popularity.
M 41 to M 45: Completion of the first catalog Early in 1765, Messier found the open cluster M 41. For a long time, this was the last entry in his observing log. The subsequent pause of four years saw his boat journey to the Netherlands in 1767 and further comet discoveries – apparently, Messier was pondering whether to publish his list of nebulae or not. In March 1769, he finally made up his mind and completed the catalog with the inclusion of several wellknown objects as his entries M 42, M 43, M 44, and M 45, listed under the date of the 4th of March 1769. All of these objects are impossible to confuse with a comet, and it remains a matter of speculation why he added them. Perhaps having a catalog with 41 objects did not satisfy Messier’s sense of symmetry, and he wanted to exceed the 42 entries in the catalog of his role-model, Lacaille. In his foreword, Messier mentioned the motivation for making a list of all nebulous patches in the sky, rather than just those which look like a comet. However, he did not include other significant objects in that respect, e.g., the double cluster h &F Persei, which apparently did not bother him much. There simply were not enough such objects left to round the number up to an even better sounding total of 50 entries. The manuscript for the first catalog was finally completed on the 16th of February 1771. It was printed in that same year for the 1774 edition of the Mémoires de l’Académie Royale des Sciences.
M 46 to M 52: Further discoveries Only three nights after the manuscript of the first catalog was finalized (19th of February 1771), Messier discovered four more objects: three more star clusters (M 46 to M 48) and the first galaxy of the Virgo cluster, M 49. Later that same year, on the 6th of June an object was discovered but its position not measured until 1779, which gave it a much later entry as number 62. Instead, on the 5th of April 1772, Messier finally found a nebula from a note of Cassini, for which he had been looking since 1764, now his M 50 – not much more than a week after his wife and newborn child had died.
25
During an observation of the Andromeda Galaxy on the 10th of August 1773, Messier discovered the companion galaxy M 110. But for reasons that are not known, he did not include this object in his catalog. The observation and a drawing were finally published in 1798 – for this, M 110 was accepted as a Messier object in the twentieth century. Also in 1773, Messier came across M 51, while he was following the comet of that year which he had discovered himself. He saw only the central part of the main galaxy. The double-nature of this object was noticed later by Méchain, whom he got to know in that year (1773). M 52 in 1774 was then for some time Messier’s last discovery; he did not engage himself again with nebulous objects until 1777.
M 53 to M 70: Completion of the second catalog version In February 1777, Messier found M 53 and the faint M 54, and M 55 followed on the 24th of July 1778, while he was looking again for an object described by Lacaille (M 55), which he had failed to find in the night of the 29th of July 1764. Meanwhile, in 1777, Bode had entered into a direct competition with Messier with his catalog of 75 nebulous objects. Then in 1779, the 6th of January, the German challenged Messier in his very domain: Bode discovered his first comet. Messier saw it only 13 nights later. The comet then happened to pass near M 56, which Messier happily added to his list. Further nebulous objects were soon found along the path of Bode’s comet by different observers: M 57 on the 31st of January 1779 by Darquier, the Virgo galaxies M 59 and M 60 on the 11th of April by Köhler (four days later independently discovered by Messier, together with M 58), and M 61 by Oriani, on the 5th of May. The latter galaxy was seen by Messier the same night, but confused with the comet; he noticed his mistake six nights later. The other galaxies of the Virgo cluster had not yet been observed. June 1779 saw the first contribution to the Messier catalog by a discovery of Méchain: M 63. In March and April 1780, Messier had a very productive phase again: he discovered M 64, M 65, M 66, M 67, and M 68. The much grown number now motivated him to publish a second version of his catalog. It was printed in the 1783 edition of the French Almanac, the Connaissance des Temps. Two more objects (M 69 and M 70) found by Messier on the 31st of August 1780, and making a pleasantly round number, were added on in the annex of the same edition.
M 71 to M 103: Méchain’s discoveries and the final catalog version Again, new discoveries were made immediately after the publication of the catalog. More than 32 new objects were observed between October 1780 and March 1781. The personal discoveries achieved by Messier were M 73 (when he was looking for M 72 of Méchain), M 84, M 86, and M 87 to M 93
26
Observations of nebulae before Messier For the earliest astronomers, nonstellar (fixed) objects had little importance and hardly any attention was paid to them. The only exception was the easily resolved and bright star cluster of the Pleiades, which played an important role in astronomical calendars and mythology. For example, the tradition of All Saints Day and Halloween is based on the culmination time of the Pleiades. Nebulae were not noticed by the ancient Greek scholars, only Hipparchus mentioned, apart from the Pleiades, the other two cloud-like objects, M 44 and h & F Persei. The great star catalog of the second century AD, the Almagest produced by Ptolemy (83–161), already contained seven objects characterized as “cloud-like” or “nebulous.” But apart from M 7, M 44, and h & F Persei, they are not real but rather chance alignments of stars that remain unresolved and therefore appear nebulous to the naked eye. Not even the two most obvious of the real nebulae, M 31 and M 42, are mentioned in the Almagest, nor elsewhere in antiquity. This demonstrates the lack of interest in such objects. The first note on M 31 came from the Persian scholar Al Sufi in the tenth century, when he worked on a revision of the Almagest. And the discovery of M 42 had to wait until the first telescopic observations in the early seventeenth century. In 1611, several astronomers discovered the Orion Nebula almost at the same time – the very first of them was Nicholas Peiresc. The first telescopes were also used for several other non-stellar objects. Galileo found that M 44 was not a nebula but a cluster of faint stars. About the same time, Simon Marius discovered M 31, which was still
unknown in Europe. After him, Giovanni Batista Hodierna (1597–1660) made a series of discoveries. His list of 19 observed objects contains nine genuine discoveries (including M 6, M 36, M 37, M 38, M 41, M 47, and perhaps M 33, and M 34), but his notes were lost and remained entirely unknown until their rediscovery in the twentieth century. For quite some time not much progress was made; nebulae were still objects of little interest. In 1647, Johannes Hevelius published one of the last large star catalogs achieved without the use of a telescope, he therein mentioned 14 “nebulous” objects, mostly taken from Ptolemy. As in the Almagest, these “nebulae” are mostly accidental stellar patterns, which are not resolved by the naked eye. However, with the advent of this widely known publication, nebulous objects gained a bit more attention for the next hundred years. In 1733, Hevelius’ original listing of 14 objects was translated from Latin into English by William Derham and supplemented with M 7 and NGC 6231. In this form, it came to Charles Messier, who tried to verify these 16 objects in 1764. Since most of them were not real, they could not be identified as a nebula through the telescope. Only Hevelius No. 14 survived as M 40, as Messier included it in his catalog, although he only saw a faint double star and no nebulous object. Not long after the work of Hevelius, M 22 (Ihle, 1665) and M 11 (Kirch, 1681) were found by telescopic observation, the first discoveries made from Germany. In England, meanwhile, Edmond Halley was quite active. Best known for his long-period comet, he had already discovered Z Cen in the southern sky in 1677. From
home, he found M 13 in 1714. In a 1715 publication, he also described M 42, M 31, M 22, and M 11. But it wasn’t until Messier’s time, when the quality of telescopes had improved sufficiently, that more progress could be made. In 1746, the Swiss aristocrat de Chéseaux (1718–1751) listed 21 observed nebulae, which include eight genuine discoveries. But as in the case of Hodierna, his notes were not published, because de Chéseaux was not a member of any important scientific society, so he was not accepted by the scientific establishment. This was different with Nicolas Louis de Lacaille (1713–1762), who presented a list of 42 nebulous objects in 1755 as a byproduct of his star survey of the southern sky. Despite the very small aperture he had used, this first real nebula catalog contained a significant number of genuine discoveries and was of very good quality, especially in terms of positional information. Certainly, it was the best example for Messier, who reprinted Lacaille’s list as an annex to his 1771 catalog. Hence, many southern objects were known before Messier’s work, while the northern sky was still almost untouched. Concurrently with Messier, Guillaume Le Gentil (1725–1792) made a few discoveries. Like Messier, he once was a student of Delisle in the Collège de France. In his publication, submitted in 1749 but not printed until 1755, Le Gentil mentioned M 32, M 8, M 41, M 36, and M 38.
Some astronomers who paved the way for Messier: Hevelius, Flamsteed, Halley, Peiresc, de Mairan, Huygens.
Hevelius “Nebulosae,” 1647 Derham’s number
Constellation Derham’s description
Modern identification
1
Andromeda
In Andromeda’s girdle
M 31
2
Cancer
Praesepe
M 44
3
Capricornus
In the forehead of Capricorn
V Cap
4
Capricornus
Another, preceding the eye of Capricorn
S Cap
5
Capricornus
Another following it
R Cap
6
Cygnus
Preceding above the Swan’s tail and last in its northern foot
Z Cyg
7
Cygnus
One of two following the Swan’s tail, outside the constellation
?
8
Hercules
At the tip of Hercules’ left foot
88 Her
9
Hercules
In the left leg of Hercules
90 Her
10
Hercules
In the head of Hercules
32, 33, 34 Oph
11
Libra
Under the beam of the western scale
], 17, 18 Lib
12
Pegasus
Following the ear of Pegasus
34, 35, 37 Peg
13
Scutum
Below the western border of the shield
?
14
Ursa Major
Above the back of Ursa Major
?
27
Visual observers after Messier From the seventeenth to the nineteenth century, visual observation at the telescope’s eyepiece was the common scientific means of documentation in astronomy. The observers would produce drawings and descriptions, which were then reproduced in professional publications. It was not until the end of the nineteenth century that emerging photographic techniques evidently became the more accurate and less subjective form of recording positions and intensities than visual observation. Nevertheless, descriptions from the great historic visual observers are still most valuable for the modern amateur for comparison with his or her own visual observations. We have to keep in mind that those historic observers could not “cheat” and look at a photograph to get some help; they depended entirely on the capabilities of their eyesight.
Frederick William Herschel (1738–1822) William Herschel was a musician, born in the German town of Hanover, who had emigrated to England. He became the first observer to undertake a systematic search for nebulae for their own sake. Most likely, he was inspired by Messier’s catalog. Within 20 years, he compiled a huge catalog of 2500 nebulae and star clusters. Herschel had produced home-made telescopes and mirrors since 1774, for himself as well as for other astronomers. For his nebula observations, which he started in 1782, he used a very large, modified Newtonian telescope with 18 inches (475mm) of aperture and 20-feet (6m) focal length. His standard magnification was 157× with a field of view of 15', with which he was systematically scanning the sky. He combed through a zone of 4 minutes to 5 minutes in right ascension with a length of 12° to 14° in declination and noted all newly
28
found objects for a later, accurate position measurement. This procedure was then repeated in a band of right ascension adjacent to the preceding field. Wanting a larger objective for this project, Herschel finished building the then largest telescope in the world in 1789, with a huge 47-inch (1.2m) metal mirror of 40-feet (12m) focal length, but it proved too bulky for scanning purposes, so he would instead use it for detailed observations of individual objects. Herschel’s first discovery, on the 7th of September 1782, was the Saturn Nebula NGC 7009. By 1785, he had found about 1000 more nebulous objects, another 1000 by 1789, and a final 500 by 1802. Hence, his 20 years of work increased the number of known nebulae by a factor of more than 20 – an immense achievement. William Herschel is probably the most industrious deep-sky observer of all time.
and the revised observations of his father into the General Catalogue (GC) of Nebulae and Star Clusters. It became the basis for the famous New General Catalogue (NGC) of 7840 entries. The latter, created by Johann Dreyer in 1888, included all the objects then known and is still in widespread use today.
William Smyth (1788–1865) The retired English admiral discovered astronomy as his hobby and built his own private observatory with a 6-inch refractor. In close contact with John Herschel, he observed numerous deep-sky objects. In 1844, he published the “Bedford Catalogue,” the “grandmother” of all deep-sky observing guides, which included descriptions of 98 nebulae and 72 star clusters. His work offers rich insights into the practice of amateur astronomy 160 years ago.
John Herschel (1792–1871)
William Lassell (1799–1880)
John diligently continued the work of his father. He shipped the venerable 18-inch telescope to South Africa, where he systematically searched the southern sky for nebulae. In the years 1834 to 1838, he discovered 1689 new objects. In 1864, he finally combined his own
This wealthy brewer and amateur astronomer from Liverpool, England, was able to spend considerably more money for his astronomical desires than his contemporaries. In 1845, he built a 24-inch Newtonian on a fork-mount, which he used to do numerous observations and drawings of nebulae. In 1858 in Liverpool, he had a reflec-
tor with a 48-inch mirror made, one of the largest telescopes of its time. He shipped it to Malta in 1861, to take advantage of the far superior observing conditions there.
William Parsons, Lord Rosse (1800–1867) The third Earl of Rosse was a rich Irish nobleman who developed an enthusiasm for observing due to his contact with John Herschel. In April 1845, after considerable experimentation with the techniques needed to build very large reflectors, he constructed his huge telescope, “Leviathan,” which had a 72-inch (1.8m) mirror. Then the largest telescope in the world, it was set up in the gardens of his Irish estate at Birr castle and was so cumbersome that several people were required to operate it. Nevertheless, the Lord himself and several assistants made a large number of observations and drawings of nebulae in the decades to follow. One of his most important discoveries was the spiral structure of some galaxies. However, this success later tricked him into seeing spiral patterns even in star clusters. The assistants of Lord Rosse were: J. Rambaut (1848), B. Stoney (1850–1852), R. Mitchell (1853–1858), S. Hunter (1860–1864), S. Ball (1866–1867), C.E. Burton (1868–1869), R. Copeland (1871–1874), J. Dreyer (1874–1878).
Heinrich d’Arrest (1822–1875)
Leo Brenner (1855–1936)
D’Arrest, a descendent of Huguenot immigrants to Germany, was director of the Copenhagen Observatory near the Danish capital. His published notes, “Siderosum Nebulorosum,” which contain observations of 1942 objects and include 321 discoveries, prove that he was a very diligent observer. For most of his work, he used the 11-inch refractor at the Copenhagen observatory.
Spiridon Gopþeviü is one of the most debated observers of all time. In 1894, he started to approach the public under his pseudonym Leo Brenner. On the Mediterranean island of Lussin, which then belonged to Austria (today the Croatian island Lošinj), he built a private observatory with a 7-inch refractor and published many incredibly detailed, but often fictitious, reports. In 1909, after he had lost almost all his credibility with professional astronomers, he simply vanished from the astronomical scene. His descriptions are relevant for the German-speaking community, though, because in 1902 he published the first ever observing guide on the deep-sky in the German language.
Léopold Trouvelot (1827–1895) This French painter received considerable recognition for his precise drawings of plants and animals. His sketches of the aurora borealis finally caught the attention of Harvard astronomers in Cambridge (USA), who invited him to hone his talents with telescopic observation. In 1875, he was hired by the US Naval Observatory in Washington (DC), where he subsequently produced more than 7000 drawings of astronomical objects – still the finest of their kind. However, after his death, Trouvelot acquired a bad reputation in the USA because he introduced the European gypsy moth, whose caterpillars have caused a lot of damage to US agriculture ever since.
Wilhelm Tempel (1821–1889) With a very humble, provincial family background in the east of Germany, he received his first recognition from abroad. His breakthrough came in 1859 when he discovered a comet and the nebula in the Pleiades that surrounds Merope – both feats were achieved with his small 4-inch refractor. In 1874, Tempel started work at the Arcetri Observatory near Florence (Italy), where he carried out numerous observations of nebulae and made 146 discoveries of new objects.
Edward Emerson Barnard (1857– 1923) This American is regarded as perhaps the best visual observer of all times. He had the combined gift of a keen eye and a well-trained, accurate perception. Coming from a very poor family background, Barnard started his career as a laboratory assistant in a photography shop and observed the night sky as an amateur astronomer. He soon became known as the discoverer of several comets. In 1887, he was hired by the Lick Observatory, where he made some spectacular discoveries with the 36-inch refractor, then the largest refractor in the world. Apart from his skills as a visual observer, he was also a very successful pioneer of deep-sky astrophotography.
29
Star chart with the observed path of the comet of 1764, according to Messier’s positional measurements.
– all other new objects were contributed by Méchain, but verified by Messier through observation and positional measurement. The last version of the catalog was supposed to have the round number of 100 entries. However, Méchain was discovering new objects in such quick succession, that Messier could not verify them all in time for the submission deadline of the manuscript. Hence, he added M 101, M 102, and M 103 to the finalized list with the remark: “From M. Méchain, have not yet been observed by M. Messier.” The objects M 108 and M 109 had been mentioned only in the note on M 97. Apparently, this third version of the catalog was prepared under considerable time pressure. It was printed already in spring 1781, for the 1784 edition of the Connaissance des Temps.
30
M 104 to M 109: After press Shortly after he received his personal copy of the third catalog from the printer, Messier made a hand-written note in it about a further discovery of Méchain's from the 11th of May 1781: M 104. Messier also added positions for the now-measured objects M 102 and M 103, as well as for M 108 and M 109 (in the note on M 97). Hence, initially, there was no indication that this would be the last version of Messier’s catalog. Also, Méchain remained active. Not only did he discover his first two bright comets on the 28th of June and the 9th of October of 1781, in July he also discovered the nebula now known as M 106. In addition, a discovery made by Méchain in March that year, M 105, had simply been overlooked in those final hectic days of work on the catalog. The next year (April 1782), M 107 was found by Méchain. Nevertheless, a new, updated version of the Messier catalog would never come. That may well be “blamed” on William Herschel.
De Chéseaux’s list of nebulae Philippe Loys de Chéseaux was a rich, Swiss nobleman living in the countryside near Lausanne, where he had his own observatory. He became known as a result of his independent discovery of comet Klinkenberg (C/1743 X1), on the 13th of December 1743. On the 13th of August 1796, he discovered another comet, C/1746 P1. Using a 2-foot (focal length) Gregorian reflector, he drew up a list of 21 star clusters and nebulae in 1746. For eight of those objects (M 4, M 16, M 17, M 25, M 35, M 71, NGC 6633, and IC 4665), he is the original discoverer.
He sent his list to his grandfather Reaumur, who was a member of the French Academy of Sciences, and who presented the list at an Academy meeting on the 6th of August, 1746. However, no printed publication followed, and de Chéseaux’s work was forgotten until its rediscovery in 1884. Messier mentioned the list in the foreword to his first catalog version, but apparently, he had no complete knowledge of it.
Star clusters: 1. M 6
Between Scorpius, Ophiuchus, and Sagittarius, there is a very beautiful one, of which the principal stars have this year RA 260° 52' 30" and southern declination 32° 1' 30". 2. IC 4665 Above the shoulder, beta of Ophiuchus, a cluster of stars of which the two principal stars have this year: RA 264° 46' 50" and southern [should read northern] dec. 6° 50' 20"; RA 264° 31' 55" and southern [should read northern] dec. 7° 00' 10". 3. NGC 6633 Near the tail of Serpens in which there is a small cluster of stars, a bit separated from the rest to the west; its RA is at 273° 32' 30" and its southern [should read northern] declination is 6° 19' 20". 4. M 16 A cluster of stars between the constellations of Ophiuchus, Sagittarius, and Antinous, of which RA is 271° 3' 10" and southern declination is 13° 47' 20". 5. M 25 Another [star cluster] between the bow and the head of Sagittarius, of which RA is about 274° 17' and southern decl. is 19° 11' 30". 6. NGC 869 7. NGC 884 Two clusters of stars in the hilt of Perseus’ sword, earlier observed by M. Flamsteed. 8. M 8 Another [star cluster] in the bow of Sagittarius, observed by the same. 9. NGC 6231 10. M 7 The last two [objects] of the catalogs of Messieurs Derham and Maupertuis. 11. M 44 That in Cancer, ordinarily called Praesepe, the position of which is known. 12. M 35 13. M 71 Two others of which I have not yet determined the positions, one above the northern feet of Gemini, and the other below and very close to Sagitta. 14. M 11 Lastly, a prodigious cluster of small stars, near one of the feet of Antinous of which RA is 279° 21' 10" and southern decl. is 6° 32' 20"; it has about 4 1/8' in diameter. These 14 nebulae contain among them almost as many stars visible in telescopes of 25 feet as the greater part of the sky contains as visible to the naked eye. Here now are the rightly styled nebulae which, when seen in the largest telescopes, never appear as anything but white clouds: 17. M 22 A third, discovered by Abraham Ihle, between the head and the bow of Sagittarius, of which I found the RA of 275° 14' 10" and southern dec. 24° 5' 30". It is 5' in diameter, it is round, of a reddish color, whereas the Andromeda Nebula is yellowish and that of Orion, transparent. 18. NGC 5139 That in Centaurus, discovered by Mr. Halley; it is invisible in Europe. 19. M 4 One which is close to Antares, of which I have found for this year, RA 242° 1' 45" and southern dec. 25° 23' 30". It is white, round and smaller than the preceding ones; I do not think it has been found before. 20. M 17 Lastly, one other nebula, which has never been observed. It has a shape quite different from the others: it has the perfect form of a ray, or of the tail of a comet, 7' long and 2' wide; its sides are exactly parallel and quite well terminated, the same for the two ends. The center is whiter than the edges. I found its RA for this year as 271° 32' 35" and its southern declination as 16° 15' 6". It makes an angle of 30° with the meridian. 21. M 13 I have not yet found that in Hercules, discovered by M. Halley. I very much hope that the Messieurs astronomers of Paris will be willing to indicate its position for me.
31
The catalog of Abbé Lacaille No.
Present designation
Con.
R.A.
Tuc
0h 33.41min
Decl.
Pos.-error
Type
–72° 4'
41'
GC
First section: Nebulae without stars Lac I.1
NGC 104
h
min
Lac I.2
NGC 2070
Dor
5 38.4
–69° 10'
5'
GN
Lac I.3
NGC 2477
Pup
7h 50.9min
–38° 37'
15'
OC
min
h
Lac I.4
NGC 4833
Mus
12 59.7
–70° 49'
4'
GC
Lac I.5
NGC 5139
Cen
13h 26.8min
–47° 29'
0'
GC
Lac I.6
M 83
Hya
h
min
–29° 52'
2'
Gx
h
min
–62° 56'
1'
OC
–40° 39'
0'
OC
min
13 37.1
Lac I.7
NGC 5281
Cen
13 46.6
Lac I.8
NGC 6124
Sco
16h 25.6min h
Lac I.9
M4
Sco
16 23.7
–26° 31'
2'
GC
Lac I.10
NGC 6242
Sco
16h 55.6min
–39° 28'
0'
OC
min
h
Lac I.11
M 69
Sgr
18 30.0
–33° 29'
1,2°
GC
Lac I.12
M 22
Sgr
18h 36.4min
–23° 55'
1'
GC
min
h
Lac I.13
(NGC 6777)
Pav
19 26.8
–71° 30'
2'
Ast
Lac I.14
M 55
Sgr
19h 40.1min
–30° 57'
2'
GC
Hor
4h 3.0min
Lacaille’s catalog of nebulae It seems astounding that the very first catalog of deepsky objects, presented in 1755 by Abbé Nicholas-Louis de Lacaille – 14 years before Messier’s first catalog of 45 objects – was actually devoted to the southern sky. In any case, Lacaille’s catalog was the first significant work of its kind, which also became widely known and accepted. Earlier object lists either had been very short (like the one by Halley), or had not reached the wider scientific community (like those of Hodierna in 1654, or de Chéseaux in 1746). Lacaille’s catalog of 42 objects was published in 1755 in the Memoirs of the French Academy of Sciences, and again in 1784 as an annex to Messier’s work. Lacaille’s
Second section: Star clusters Lac II.1 Lac II.2
Collinder 140
CMa
–44° 28'
0'
Ast
h
min
–34° 09'
2,1°
OC
h
min
7 26.2
Lac II.3
NGC 2516
Car
7 58.9
–60° 50'
9'
OC
Lac II.4
NGC 2546
Pup
8h 11.2min
–37° 13'
28'
OC
h
min
Lac II.5
IC 2391
Vel
8 38.8
–53° 6'
17'
OC
Lac II.6
Collinder 203
Vel
8h 46.8min
–42° 16'
19'
OC
min
–51° 43'
2'
OC
–58° 13'
2'
OC
h
Lac II.7
NGC 3228
Vel
10 21.4
Lac II.8
NGC 3293
Car
10h 35.9min h
min
Lac II.9
IC 2602
Car
10 43.1
Lac II.10
NGC 3532
Car
11h 6.5min
Lac II.11
-
h
Cen
11 22 h
min
–64° 24'
1' (37")
OC
–58° 40'
10'
OC
–58° 21'
2'
Ast
min
Lac II.12
NGC 4755
Cru
12 53.7
–60° 22'
1'
OC
Lac II.13
NGC 6231
Sco
16h 54.2min
–41° 50'
1'
OC
3'
OC
Lac II.14
M7
h
min
Sco
17 53.8
–34° 45'
Third section: Stars with nebulosity Lac III.1
nonexistent
Pic
5h 3.4min
–49° 30'
Lac III.2
NGC 2547
Vel
8h 10.7min
–49° 15'
7'
OC
Lac III.3
IC 2395
Vel
8h 42.4min
–48° 6'
2'
OC
–57° 0'
4'
OC
Lac III.4
IC 2488
Vel
h
min
9 27.8 h
min
Single star
Lac III.5
Collinder 228
Car
10 44.0
–60° 7'
3'
OC
Lac III.6
NGC 3372
Car
10h 44.3min
–59° 30'
10'
GN
Lac III.7
NGC 3766
Cen
11h 36.2min
–61° 37'
0'
OC
Lac III.8
NGC 5662
Cen
14h 35.3min
–56° 34'
4'
OC
h
min
Lac III.9
-
Cir
15 22.7
–59° 10'
2'
Ast
Lac III.10
NGC 6025
TrA
16h 3.8min
–60° 30'
5'
OC
min
h
Lac III.11
NGC 6397
Ara
17 40.7
–53° 42'
2'
GC
Lac III.12
M6
Sco
17h 40.1min
–32° 13'
3'
OC
–24° 22'
1'
OC+GN
–56° 53'
1'
Ast
Lac III.13 Lac III.14
M8 -
Sgr Ind
h
min
18 3.9 h
21 31.1
min
Ast = asterism. The coordinates are the positions given by Lacaille as for equinox 2000.0.
32
1' (52")
The frontispiece of Lacaille’s catalog depicts a contemporary view of the Paris Observatory.
list has three sections: “Nebulae without Stars,” “Star Clusters,” and “Stars with Nebulosity.” Incidentally, each of the sections contains exactly 14 objects. This equipartition already puzzled Kenneth Glyn Jones in the 1960s. Perhaps it satisfied a baroque desire for symmetry. Lacaille himself remarked on his list as follows: “I have found a large number of nebulae of these three types in the southern sky, but I would not believe that I have noticed all of them; in particular of the first and third type, because these are visible only after dusk and in the absence of the Moon. Nevertheless, I hope that this list is more or less complete for the most remarkable objects of the three types.” For his task, Lacaille had only very humble optical equipment. He wrote: “I have wished dearly to present a more detailed and informative work. But the simple refractors available to me at the Cape of Good Hope, of 15 and 18 inches [focal length], were neither adequate nor sufficient for this kind of observation.” Since his telescopes were probably non-achromatic with focal ratios of around f/10, their apertures cannot have exceeded 40mm (1½ inches). The fact that Lacaille could not resolve ZCentauri (NGC 5139) into individual stars, or open clusters like NGC 6124, reveals the poor quality of his instruments.
Messier’s drawing of M 42, published in the annex of the first catalog. For this observation, Messier used an achromatic Dollondrefractor with an aperture of 40 lines (90mm), a focal length of 3.5 feet (1.14m), and a magnification of 68×, on the nights of the 25th and 26th of February, and the 19th, 23rd, 25th, and 26th of March 1771. The circular border represents the edge of the actual field of view, about 30'. South is above.
The German-born musician, who had emigrated from Hanover to England, became famous for a discovery he made on the night of the 13th of March 1781 – only four days after the last official entry to Messier’s catalog. At first, Herschel took his new object for a comet, and so he asked Messier, the famous expert on comets, for his opinion. Messier observed the new object, measured its position over several nights, and had his friend de Saron calculate the orbit. The result was sensational: Herschel had found a new planet, Uranus. With the fame of this discovery, Herschel received a royal salary, which finally allowed him to concentrate fully on astronomical work. In 1782, he began an extensive search for new nebulous objects and, due to both his superior Newtonian telescopes and his dedication, made about 1000 new discoveries by 1786. By the end of that project in 1802, Herschel had compiled a huge list of about 2500 nebulae. It was the Messier catalog (he received his copy on the 7th of December 1781) that almost certainly gave him the idea. At the same time, the unlucky Messier had to abandon all his work after his serious accident (6th
of November 1781). After a long, painful recovery, he did not resume his search for new nebulae – in 1802 he described why: After me, the famous Herschel published a catalog of 2000 [nebulae] which he had observed. Unveiling the sky in his way, with instruments of large aperture, is not useful for comet seeking. Hence, my objective is different from his: I only need the nebulae that are visible in a telescope of 2 ft [focal length]. I have observed more, meanwhile. I will publish them in the future, organized by right ascension, for the sake of finding them more easily, and so that those who are looking for comets have less uncertainty. But such a final publication never came to be.
33
words. There is now broad consensus about most identities, except the case of M 102.
M 47
Examples of Messier’s observing results: a drawing of Saturn, the occultation of Saturn by the Moon on the 18th of February 1775, and the sunspots of the 17th of July 1777.
Messier’s position lies in a field without any recognizable star clusters. Hence, astronomers after Messier long believed that M 47 did not exist. However, in 1959, T.F. Morris was able to prove an assumption that Oswald Thomas made in 1934: Messier made a sign-related mistake in his calculation of the position. As a curious result, M 47 has two NGC entries: a false one, NGC 2478, in its wrong position, and the true one, NGC 2422, with the correct coordinates from Herschel.
M 48
The “missing” Messier objects Messier’s catalog was of high quality and contained relatively few errors. For each object, Messier took the position relative to a bright neighbor star. Furthermore, a large number of objects was observed more than once, especially for the third version of the catalog. Nevertheless, Messier could not entirely avoid making mistakes. Consequently, there are a few objects for which the identification remained ambiguous and matter of debate. Glyn Jones called these the “missing Messier objects,” which has become the adopted choice of
34
The same night he recorded M 47, Messier made another simple calculation mistake with M 48, putting it exactly 5° too far south. Again, Oswald Thomas and T.F. Morris found the right identity: NGC 2548 has now been commonly accepted as M 48.
M 91 With this galaxy, a positional error is also the most likely explanation. There is no sufficiently bright galaxy at the position given by Messier, only a lot of faint galaxies of the Virgo Cluster. Owen Gingerich suggested that M 91 may just be an accidentally repeated observation of M 58, a galaxy only 2.7° south of Messier’s position. But in 1969, W.C. Williams showed that Messier used a galaxy as his reference point for M 91 (there are hardly any bright stars in this field) and that he sim-
Bode’s catalog of nebulae In 1777, three years after Messier presented his first catalog, the Berlin astronomer Johann Elert Bode undertook the same endeavor. In his publication “On several newly discovered nebulous stars and a complete listing of all known so far” he wrote: “I wanted to search for nebulous stars [objects] with diligence. Since I had the pleasure to discover a number of new ones, which until then, at least, I had not found with any other astronomer, I herewith wish to communicate them.” With the use of several different sources, including Messier’s first catalog, Bode managed to collect 75 objects north of –35° declination. However, the diverse origin of the data was also the problem with Bode’s catalog. We only know with certainty of eleven objects that Bode observed himself. Of these, M 53, M 81, and M 82 were his own discoveries. All of the other objects had been copied from the literature without any verification, as Bode admits: “I have to add that I myself have not yet had the opportunity to observe all of the nebulae discovered by other astronomers.” As an example, this explains why M 8 has been listed three times – with different positions. The problem of non-verified entries was the death-sentence for Bode’s list, despite his good reputation as an astronomer. He printed it once again in 1782 in his star atlas “Vorstellung der Gestirne,” expanded with some new discoveries (including M 92, IC 4665, and the star pattern near F Dra known as the “little Cassiopeia”), but the catalog never achieved widespread international use.
The catalog of Johann Elert Bode
The catalog of Johann Elert Bode
Bode’s No.
Present designation
Original source
Bode’s No.
Present designation
Original source
1
?
own observation
39
M6
Lacaille
2
M 32
Messier
40
90 Her
Hevelius
3
M 31
Messier
41
M7
Lacaille
4
Muster 1° W O Cas
own observation
42
M 23
Messier
5
M 33
Messier
43
4 Sgr
Flamsteed
6
55 And
Flamsteed
44
5 Sgr
Flamsteed
7
M 34
own observation
45
M8
Le Gentil
8
M 45
–
46
M 69
Lacaille
9
M 38
Messier
47
M 20
Messier
10
M 42
Messier
48
7 Sgr
Flamsteed
M8
Messier
11
M1
Messier
49
12
M 36
Messier
50
M 21
Messier
13
M 37
Messier
51
M 24
Messier
14
M 35
Messier
52
M 16
Messier
15
M 41
Messier
53
M 18
Messier
16
M 50
own observation
54
M 17
Messier
17
M 81
own observation
55
J Sct
Hevelius
18
M 82
own observation
56
M 25
Messier
19
Cr 140
Lacaille
57
M 22
Lacaille
20
M 44
–
58
M 28
Messier
21
NGC 2477
Lacaille
59
M 26
Messier
22
NGC 2546
Lacaille
60
Q1 Sgr
Flamsteed
Messier
61
Q Sgr
Flamsteed
M 11
Messier Lacaille
23
M 40
2
24
M 40
Hevelius
62
25
M 51
own observation
63
M 55
26
M 53
own observation
64
V Cap
Hevelius
27
M 83
own observation
65
S Cap
Hevelius
28
[1 , [2, 17, 18 Lib
Hevelius
66
R Cap
Hevelius
29
M5
Messier
67
M 27
Messier
30
M 13
Messier
68
M 30
Messier
31
M4
Lacaille
69
M 29
Messier
32
M 12
own observation
70
M2
Messier
33
M 10
own observation
71
M 15
Messier
34
32, 33, 34 Oph
Hevelius
72
Z
Cyg
Hevelius
35
M 19
Messier
73
34, 35, 37 Peg
Hevelius
36
M9
Messier
74
?
Hevelius
37
M 14
Messier
75
M 39
Messier
38
88 Her
Hevelius
1+2
35
Three people had a significant influence on the extension of the Messier catalog: Camille Flammarion (1842–1925, French writer of popular astronomy), Helen Sawyer Hogg (1905–1993, professional Canadian astronomer), and Oswald Thomas (1882–1963, founder of the planetarium of Vienna).
ply confused M 89 with M 58. This yields the real identity of M 91 as NGC 4548.
M 102 The identity of this object has remained a matter of debate to the present day. Many modern US publications regard this object as “missing,” while most European sources identify it with the galaxy NGC 5866. This discussion has its origin in a letter, which Pierre Méchain wrote two years after the third version of the Messier catalog was completed, on the 6th of March 1783. He sent it to Bernoulli in Berlin, because Messier’s list of nebulae was also published in the Berlin Astronomical Almanac. Méchains letter was printed in the 1786 edition of the same almanac. In it, a passage reads: I would only like to add that Nr. 101 & 102 on p. 267 of the Connaissances des Temps for 1784 are nothing else than one and the same nebula, which was taken for two because of an error in the charts. In other words, Méchain said that M 102 was his accidentally repeated observation of M 101. Hartmut Frommert, however, came up with some serious doubts. Firstly, the descriptions of M 101 and M 102 given in the catalog differ from each other. And then, like M 103, M 102 had actually been observed and measured by Messier himself, as we know from his handwritten positions in his personal copy of the printed catalog. For M 103, there is an error of 1°, while there is no object near the position he noted for M 102. However, if he had made a simple mistake with the calculation, again by 5° as with M 48, but this time in right ascension, then there would be an object in the right place, which also
36
matches the description of M 102: NGC 5866. Hence, it is quite possible that Méchain accidentally observed M 101 twice, indeed, but that Messier then, while looking for the acclaimed object, found a real nebula – M 102 alias NGC 5866 was probably his last nebula discovery.
The supplementary Messier objects The original Messier catalog of 1784 contains 103 explicit entries. Nevertheless, today’s commonly accepted number of Messier objects is 110. The supplements have been added on in the twentieth century, according to evidence for objects observed by Messier but not (or not explicitly) included in his catalog. An important role is played by the above-mentioned letter of Méchain to Bernoulli, because it contains comments on further observed objects. The other important source is Messier’s personal copy of the catalog, which contains his handwritten notes. In 1924, Camille Flammarion discovered and bought that very copy, and he found Messier’s notes in it. One of them is about a further “very faint nebula in Virgo.” In his letter, Méchain wrote about this object and three others:
M 104 On 11th May 1781, I discovered a nebulous patch above Corvus which did not appear to me to contain single stars. It has a weak light and is difficult to find if the wires of the micrometer are illuminated. I compared it to Spica this day and the following and inferred the right ascension as 187° 9' 42", the southern
Discoverers of the Messier objects
Discoverers of the Messier objects
Discoverers of the Messier objects
Name
Discoverer
Messier’s Observation
Name
Discoverer
Messier’s Observation
Name
Discoverer
Messier’s Observation
M1
Bevis 1731
August 28th, 1758
M 37
Hodierna 1654
September 2nd, 1764
M 74
Méchain 1780
October 18th, 1780
M2
Maraldi 1746
September 11th, 1760
M 38
Hodierna 1654
M 75
Méchain 1780
October 5th, 1780
M3
Messier 1764
May 3rd, 1764
September 25th, 1764
M 76
Méchain 1780
October 21th, 1780
M 39
Messier 1764
October 24th, 1764
M 77
Méchain 1780
December 17th, 1780
M 40
Messier 1764
October 24th, 1764
M 78
Méchain 1780
December 17th, 1780
M 41
Hodierna 1654
January 16th, 1765
M 79
Méchain 1780
December 17th, 1780
M 80
Messier 1781
January 4th, 1781
M 81
Bode 1774
February 9th, 1781
M 82
Bode 1774
February 9th, 1781
M 83
Lacaille 1752
February 17th, 1781
M 84
Messier 1781
March 18th, 1781
M 85
Méchain 1781
March 18th, 1781
M 86
Messier 1781
March 18th, 1781
M 87
Messier 1781
March 18th, 1781
M 88
Messier 1781
March 18th, 1781
M 89
Messier 1781
March 18th, 1781
M 90
Messier 1781
March 18th, 1781
M 91
Messier 1781
March 18th, 1781
M 92
Bode 1777
March 18th, 1781
M 93
Messier 1781
March 20th, 1781
M 94
Méchain 1781
March 24th, 1781
M 95
Méchain 1781
March 24th, 1781
M 96
Méchain 1781
March 24th, 1781
M 97
Méchain 1781
March 24th, 1781
M 98
Méchain 1781
April 13th, 1781
M 99
Méchain 1781
April 13th, 1781
M 100
Méchain 1781
April 13th, 1781
M4 M5 M6 M7 M8 M9 M 10 M 11 M 12 M 13 M 14 M 15 M 16 M 17 M 18 M 19 M 20 M 21 M 22 M 23 M 24 M 25 M 26 M 27 M 28
de Chéseaux 1746 Kirch 1702 Hodierna 1654 Ptolemy 130 Flamsteed 1680 Messier 1764 Messier 1764 Kirch 1681 Messier 1764 Halley 1714 Messier 1764
th
May 8 , 1764 May 23rd, 1764 rd
May 23 , 1764
th
May 23rd, 1764
M 42
Peiresc 1611
March 4 , 1769
May 23rd, 1764
M 43
de Mairan 1744
March 4th, 1769
M 44
–
March 4th, 1769
May 29th, 1764
M 45
–
March 4th, 1769
May 30th, 1764
M 46
Messier 1771
February 19th, 1771
th
May 28 , 1764
th
May 30th, 1764
M 47
Hodierna 1654
February 19 , 1771
June 1st, 1764
M 48
Messier 1771
February 19th, 1771
M 49
Messier 1771
February 19th, 1771
st
June 1 , 1764
th
June 3rd, 1764
M 50
Cassini 1711
April 5 , 1772
de Chéseaux 1746
June 3rd, 1764
M 51
Messier 1773
October 13th, 1773
de Chéseaux 1746
rd
M 52
Messier 1774
September 7th, 1774
M 53
Bode 1775
February 26th, 1777
M 54
Messier 1778
July 24th, 1778 th
Maraldi 1746
June 3 , 1764
Messier 1764
June 3rd, 1764
Messier 1764
th
Messier 1764 Messier 1764 Ihle 1665 Messier 1764 Messier 1764
June 5 , 1764 June 5th, 1764
M 55
Lacaille 1752
July 24 , 1778
June 5th, 1764
M 56
Messier 1779
March 19th, 1779
M 57
Darquier 1779
January 31st, 1779
June 20th, 1764
M 58
Messier 1779
April 15th, 1779
June 20th, 1764
M 59
Köhler 1779
April 15th, 1779
th
June 5 , 1764
th
June 20th, 1764
M 60
Köhler 1779
April 15 , 1779
Messier 1764
June 20th, 1764
M 61
Oriani 1779
May 11th, 1779
Messier 1764
th
M 62
Messier 1771
June 7th, 1771
de Chéseaux 1746
Messier 1764
July 12 , 1764
th
July 27th, 1764
M 63
Méchain 1779
June 14 , 1779
Pigott 1779
March 1st, 1780
M 29
Messier 1764
July 29th, 1764
M 64
M 30
Messier 1764
August 3rd, 1764
M 65
Messier 1780
March 1st, 1780
M 66
Messier 1780
March 1st, 1780
M 67
Köhler 1779
April 6th, 1780
M 68
Messier 1780
April 9th, 1780
M 69
Lacaille 1752
August 31st, 1780
M 70
Messier 1780
August 31st, 1780
M 31 M 32
Al Sufi 964 Le Gentil 1749
rd
(1757) August 3 , 1764 (1757) August 3rd, 1764
M 33
Messier 1764
August 25th, 1764
M 34
Messier 1764
August 25th, 1764
M 71
de Chéseaux 1746
October 4 , 1780
M 35
de Chéseaux 1746
August 30th, 1764
M 72
Méchain 1780
October 4th, 1780
M 36
Hodierna 1654
September 2nd, 1764
M 73
Messier 1780
M 101
Méchain 1781
1781
M 102
Méchain 1781
1781
M 103
Méchain 1781
1781
M 104
Méchain 1781
May 11th, 1781
M 105
Méchain 1781
not observed
M 106
Méchain 1781
not observed
M 107
Méchain 1782
not observed
M 108
Méchain 1781
March 24th, 1781
M 109
Méchain 1781
March 24th, 1781
M 110
Messier 1773
August 10th, 1773
th
th
October 4 , 1780
37
declination 10° 24' 49". It is not tabulated in the Connoissance des Temps.
M 105 M. Messier thereat reports [in the catalog of 1774] p. 264 and 265, two nebulous stars, which I found in the Lion. I could not find fault with the noted positions, which were obtained by comparing them to Regulus. But there is a third a bit to the north, which is more vivid than the two preceding. I discovered it on March 24th, 1781, 4 or 5 days after I found the two others. On April 10th, I compared its position with J, obtaining a right ascension 159° 3' 45" and its southern declination 13° 43' 58".
M 106 In July 1781 I found another nebulous patch near the Great Bear next to the star No. 3 of the Hunting Dogs and 1° farther south, I estimated its right ascension 181° 40' and the northern declination approximately 49°. I will shortly try to determine the exact position of the same.
M 107 In April 1782 I discovered a small nebulous patch on the left shank of Ophiuchus between the stars ] and T, whose position I have not yet observed closely. In 1947 Helen Sawyer Hogg, who rediscovered the reprint of Méchains letter, suggested adding these four objects to the official Messier list in the order in which they are described. The printed catalog already mentioned M 108 and M 109 implicitly, in the note on M 97. These discoveries are also mentioned in the letter of Méchain, see below. This led Owen Gingerich to suggest, in 1953, adding them to the official Messier list, too.
38
M 108, M 109 Page 265 No. 97. A nebulous patch near E in the Great Bear. M. Messier remarks on two others, while noting its position, which I discovered as well and of which one is close to it, the other lies near J in the Great Bear, I have not been able to determine their positions yet. The last supplemental object (M 110), the second companion galaxy of M 31, was made an official Messier object by Kenneth Glyn Jones. As a matter of fact, Messier had already observed and sketched that dwarf galaxy in 1773. But for unknown reasons, he did not include it in his catalog, and his observing notes were published only in 1798, in the 1801 edition of the Connaissance des Temps. Did Messier and Méchain find any other objects? Apart from the above-cited hints given by Messier, there is also supporting evidence in Méchain’s letter to Bernoulli: On page 262 and 263 [of his last catalog version], M. Messier mentions several nebulous patches in the Virgin which I have indicated to him. But, there are more of them in the said area, which he did not see, and of which I will determine the positions, as soon as I have a convenient observing place, which will not be delayed too much. However, like Messier, Méchain did not continue with his nebula search. Apparently, he never found “a more convenient observing place,” and he was soon to become involved in other demanding work.
The catalog
Messier’s catalog exists in three versions: 1. First version from 1771, published in the Mémoires de l’Académie des Sciences, 1774 edition, objects 1 to 45. 2. Second version from 1780, published in the Connaissance des Temps, 1783 edition, objects 1 to 68. 3. Third version from 1781, published in the Connaissance des Temps, 1784 edition, objects 1 to 103. The following descriptions are a translation of the notes of the last version (from 1781). For each object, Messier also gives the date of his observation (which also is the equinox for the position), the right ascension in hours as well as in degrees, the declination in degrees, and (for most but not all objects) the angular diameter. Positive declinations are indicated by an “A,” negative by a “B.” For many objects discovered by Méchain, Messier lists both positional measurements, his and Méchain’s. The translation tries to maintain the character of the old-fashioned language, as well as Messier’s very individualistic use of a “:” for a “;.” Messier also indicates his other publications, referring to himself as “M.[onsieur] Messier.” The telescopes are characterized by their focal length.
The first catalog page of Messier’s third version from 1781 with the objects M 1 to M 5. For each object, the entries are the date of observation, object number, right ascension in h/min/s and deg/min/s, declination and diameter in degree/arcmin.
39
Table of the nebulae and, consequently, also the star clusters, which are found among the stars above the horizon of Paris, observed from the Observatory of the Navy. 1
Sep 12th 1758
5h 20min 2s
80° 0' 33"
Sep 11th 1760
21h 21min 8s
320° 17' 0"
1° 47' 0"A
0° 4'
Nebula without star in the head of the Water-Bearer, the center of it is brilliant, and the light which surrounds it is round; it resembles the fine Nebula which is found between the head and the bow of the Archer, it is very well seen in a refractor of two feet, placed on the parallel of a of the Water Bearer. M. Messier reported this nebula on the Chart of the path of the Comet observed in 1759, Mem. Acad. year 1760, page 464. M. Maraldi had seen this nebula in 1746, while observing the Comet that appeared in that year. 3
May 3rd 1764
13h 31min 25s
202° 51' 19" 29° 32' 57"B
0° 3'
Nebula discovered between the Herdsman & one of the Hunting Dogs of Hevelius; it does not contain any star, its center is brilliant & and its light fades insensibly, it is round; in a good sky one can see it with a refractor of one foot; it is reported on the Chart of the Comet observed in 1779. Memoirs of the Academy of the same year. Re-observed on March 29th 1781, always very beautiful. 4
May 8th 1764
16h 9min 8s
242° 16' 56" 25° 55' 40"A
0° 2½'
Cluster of very small stars; with a weak refractor it is seen in the form of a nebula; this star cluster is placed near Antares & at its parallel. Observed by M. de la Caille, & reported in his Catalogue. Re-observed on January 30th & March 22nd 1781. 5
May 23rd 1764
15h 6min 36s
226° 39' 4"
2° 57' 16"B
0° 3'
Fine Nebula discovered between the Scales & the Serpent, near the star of the Serpent, of the sixth magnitude, which is the fifth according to the Catalogue of Flamsteed: it does not contain any star; it is round, & one can see it very well, in a good sky, with a simple refractor of one foot. M. Messier reported it on the Chart of the Comet of 1763. Mem. Acad. year 1774, page 40. Re-observed on Sept. 5th 1780, January 30th & March 22nd 1781. 6
May 23rd 1764
17h 24min 42s 261° 10' 39"
32° 10' 34"A
0° 15'
Cluster of small stars between the bow of the Archer & the tail of the Scorpion. With the naked eye, this cluster seems to form a nebula; but with the smallest instrument which is employed to examine it, one sees a cluster of small stars.
40
May 23rd 1764
17h 38min 2s
264° 30' 24" 34° 40' 34"A
0° 30'
Cluster of more considerable stars than the previous; this cluster appears to the naked eye like a nebula, it is little away from the previous, placed between the bow of the Archer & the tail of the Scorpion.
21° 45' 17"B
Nebula below the southern horn of the Bull, does not contain any star; it is a whitish light, elongated in the shape of a candle’s light, discovered while observing the Comet of 1758. See the Chart of this Comet, Mem. Acad. year 1759, page 188; observed by Doctor Bevis about 1731. It is reported on the English star Atlas. 2
7
8
May 23rd 1764
17h 49min 58s 267° 29' 30" 24° 21' 10"A
0° 30'
Cluster of stars which appears in the form of a nebula when it is viewed with a simple refractor of three feet; but with an excellent instrument one does notice only a great number of small stars; near this cluster is a quite brilliant star, surrounded by a very faint light; this is the ninth star of the Archer, of the seventh magnitude, according to Flamsteed: this cluster appears in an elongated shape, which extends from North-east to South-west, between the bow of the Archer & the right foot of Ophiuchus. 9
May 28th 1764
17h 5min 22s
256° 20' 36" 18° 13' 26"A
0° 3'
Nebula, without star, in the right leg of Ophiuchus; it is round & its light faint. Re-observed on March 22nd 1781. 10
May 29th 1764
16h 44min 48s 251° 12' 6"
3° 42' 18"A
0° 4'
Nebula, without star, in the girdle of Ophiuchus, near the thirtieth star of that constellation, of sixth magnitude according to Flamsteed. This nebula is fine & round; one can see it only difficultly with a simple refractor of three feet. M. Messier reported it on the second Chart of the path of the Comet of 1769. Mem. Acad. year 1775, plate IX. Reobserved on March 6th 1781. 11
May 30th 1764
18h 30min 23s 279° 35' 43" 6° 31' 1"A
0° 4'
Cluster of a great number of small stars, near the star K of Antinous, that cannot be seen except in good instruments; with a simple refractor of three feet it resembles a Comet: this cluster is mingled with a faint light; in this cluster there is a star of 8th magnitude. M. Kirch observed it in 1681. Transact. Philos. No. 347, page 390. It is reported in the great English Atlas. 12
May 30th 1764
16h 34min 53s 248° 43' 10" 2° 30' 28"A
0° 3'
Nebula discovered in the Serpent, between the arm & the left side of Ophiuchus: this nebula does not contain any star, it is round & its light faint; near that nebula is a star of ninth magnitude. M. Messier reported it on the second Chart of the Comet observed in 1769. Mem. Acad. 1775, pl. IX. Re-observed on March 6th 1781. 13
Jun 1st 1764
16h 3min 15s
248° 18' 48" 36° 54' 44"B
0° 6'
Nebula without star, discovered in the girdle of Hercules; it is round & brilliant, the center brighter than the borders, one perceives it with a refractor of one foot; it is near two stars, both of 8th magnitude, one of them above & the other below: the nebula has been determined by comparing it with H of Hercules. M. Messier reported it on the Chart of the Comet of 1779, included in the Memoirs of the Academy, of the year 1784. Seen by Halley in 1714. Re-observed on Jan. 5th & 30th 1781. It is reported in the English star Atlas.
14
Jun 1st 1764
17h 25min 14s 261° 18' 29" 3° 5' 45"A
0° 7'
Nebula without star, discovered in the garment covering the right arm of Ophiuchus, & and placed on the parallel of of the Serpent; this nebula is not large, its light is faint, because of this it can be seen with an ordinary refractor of three & a half feet; it is round. Near it is a small star of the ninth magnitude; its position was determined by comparing it with of Ophiuchus, & M. Messier reported its position on the Chart of the Comet of 1769. Memoirs of the Academy, year 1775, plate IX. Re-observed on March 22nd 1781. 15
Jun 3rd 1764
21h 18min 41s
319° 40' 19" 10° 40' 3"B
0° 3'
Nebula without star, between the head of Pegasus & that of the small Horse; it is round, the center in it is brilliant, its position determined by comparing it with d of the small Horse. M. Maraldi, in the Memoirs of the Academy of 1746, speaks of this nebula: “I have seen, he said, between the star H of Pegasus & E of the small Horse, a star-nebula quite bright, that is composed of several stars; its right ascension is 319d 27' 6", & its southern declination is 11d 2' 22". 16
Jun 3rd 1764
18h 5min 0s
271° 15' 3"
13° 51' 44"A
Jun 3rd 1764
18h 7min 3s
271° 45' 48"
16° 14' 44"A
0° 5'
Train of light without stars, of five to six minutes in size, in the shape of a spindle, & a little bit like that in the girdle of Andromeda, but of a very faint light; there are two telescopic stars among & placed parallel to the Equator. In a good sky, one can see it very well with a simple refractor of three & a half feet. Re-observed March 22nd 1781. 18
Jun 3rd 1764
18h 6min 16s
271° 34' 3"
17° 13' 14"A
0° 5'
Cluster of small stars, a bit below the nebula above, No. 17, surrounded by a slight nebulosity, this cluster is less apparent than the previous, No. 16: with a simple refractor of three feet & a half, this cluster appears in the form of a nebula: but with a good refractor one only sees stars. 19
Jun 5th 1764
16h 48min 7s
252° 1' 45"
25° 54' 46"A
0° 3'
Nebula without stars, on the parallel of Antares, between the Scorpion & the right foot of Ophiuchus: this nebula is round; it is seen very well with a simple refractor of three & a half feet; the nearest known star to that nebula is the twenty-fifth of Ophiuchus, 6th magnitude, acc. Flamsteed. Re-observed on March 22nd 1781. 20
Jun 5th 1764
17h 48min 16s 267° 4' 5"
22° 59' 10"A
Cluster of stars, a little above the Ecliptic, between the bow of the Archer & the right foot of Ophiuchus. Re-observed on March 22nd 1781. 21
Jun 5th 1764
17h 50min 7s
22
Jun 5th 1764
18h 21min 55s
275° 28' 39" 24° 6' 11"A
0° 6'
Nebula, below the Ecliptic, between the head & the bow of the Archer, near a star of seventh magnitude, the twenty-fifth of the Archer, according to Flamsteed, this nebula is round, does not contain any star, & and can be seen very well with a simple refractor of three feet & a half; the star O of the Archer served for the determination. Abraham Ihle, German, discovered it in 1665, while observing Saturn. M. le Gentil observed it in 1747, & and he made an engraving of it, Memoirs of the Academy, year 1759, page 470. Re-observed on March 22nd 1781: it is reported in the English Atlas. 23
Jun 20th 1764
17h 42min 51s
265° 42' 50" 18° 45' 55"A
0° 15'
Cluster of stars, between the extremity of the bow of the Archer & the right foot of Ophiuchus, very near the star 65 of Ophiuchus, according to Flamsteed. The stars of the cluster are very near each other. Its position determined with P of the Archer.
0° 8'
Cluster of small stars, mingled with a faint light, near the tail of the Serpent, at small distance from the parallel of ] of that constellation; with a weak refractor it appears in the form of a nebula. 17
de according to Flamsteed. The stars of these two clusters are of the eighth to ninth magnitude, surrounded by nebulosity.
267° 31' 35" 22° 31' 25"A
Cluster of stars, near the previous; the nearest known neighboring star of these two clusters is the eleventh of the Archer, seventh magnitu-
24
Jun 20th 1764
18h 1min 44s
270° 26' 0"
18° 26' 0"A
1° 30'
Cluster of stars near the stars n & o of Antinous, among them is one of more light: with a telescope of three feet they cannot be distinguished, one has to employ a good instrument. This cluster does not contain any nebulosity. 25
Jun 20th 1764
18h 17min 40s 274° 25' 0"
19° 5' 0"A
0° 10'
Cluster of small stars in the neighborhood of the two previous clusters, between the head & the extremity of the bow of the Archer: the nearest known star to this cluster is the 21st star of the Archer, sixth magnitude, according to Flamsteed. The stars of this cluster are easily seen with a simple refractor of three feet; no nebulosity can be perceived. Its position was known by the star P of the Archer. 26
Jun 20th 1764
18h 32min 22s 278° 5' 25"
9° 38' 14"A
0° 2'
Cluster of stars near the stars n & o of Antinous, among them is one of more light: with a telescope of three feet they cannot be distinguished, one has to employ a good instrument. This cluster does not contain any nebulosity. 27
Jul 12th 1764
19h 49min 27s 297° 21' 41"
22° 4' 0"B
0° 4'
Nebula without star, discovered in the Fox, between the two forelegs, & very near the 14th star of this constellation, 5th magnitude according to Flamsteed; it is well seen with a simple refractor of 3 feet & a half: it appears in an oval shape, & does not contain any star. M. Messier reported its position on the Chart of the Comet of 1779, which will be engraved for the volume of the Acad. of the same year. Re-observed on January 31st 1781. 28
Jul 27th 1764
18h 9min 58s
272° 29' 30" 24° 57' 11"A
0° 2'
Nebula discovered in the upper part of the bow of the Archer about one degree from the star J & little distant from the fine nebula which
41
is between the head & arc. It does not contain any star; it is round, it cannot be observed without difficulty with a simple refractor of 3 feet ½. Its position was determined with J of the Archer. Re-observed on March twentieth 1781. 29
Jul 29th 1764
Aug 3rd 1764
21h 27min 5s
321° 46' 18" 24° 199' 4"A
0° 2'
Nebula discovered below the tail of the Capricorn, very near the 41 star of that constellation, 6th magnitude, according to Flamsteed. It can be seen with difficulty with a simple refractor of 3 feet ½. It is round & does not contain any star; its position determined by ] of the Capricorn. M. Messier reported it on the Chart of the Comet of 1759. Mem. Acad. 1760, pl. II.
36
Aug 3 1764
h
0 29
min
46
s
7° 26' 32"
39° 9' 32"B
0° 40'
The beautiful nebula in the girdle of Andromeda, in the shape of a spindle; M. Messier examined it with different instruments, & did not recognize any star: it resembles two cones or pyramids of light opposed by their base, the axis of which is in direction North-west to South-east; the two points of light or apexes are about 40 minutes of a degree apart; the common base of the two pyramids 15 minutes. This nebula was discovered in 1612, by Simon Marius, & observed since then by different astronomers. M. le Gentil gave a drawing of it in the Memoirs of the Academy of 1759, page 453. It is reported in the English Atlas. 32
Aug 3rd 1764
0h 29min 50s
7° 27' 32"
38° 45' 34"B
0° 2'
Small nebula without stars, below & by several minutes off that in the girdle of Andromeda; this small nebula is round, the light fainter than that of the girdle. M. le Gentil discovered it on October 29th 1749. M. Messier viewed it, for the first time, in 1757, & did not recognize any change. Aug 25th,1764
1h 40min 37s
20° 9' 17"
29° 32' 25"B
0° 15'
Nebula discovered between the head of the northern Fish & the great Triangle, at a small distance from a star of 6th magnitude: the nebula is of a whitish light, of almost equal density, however a little brighter for two thirds of its diameter, & does not contain any star. It can be seen difficultly with a simple refractor of one foot. Its position determined by comparing it with D of the Triangle. Re-observed on Sept. 27th 1780. 34
Aug 25th 1764
2h 27min 27s
36° 51' 37"
41° 39' 32"B
0° 15'
Cluster of small stars, between the head of the Medusa & the left foot of Andromeda, nearly on the parallel of J: with a simple refractor of 3 feet the stars can be distinguished. Its position was determined with E of the head of the Medusa.
42
24° 33' 30"B
0° 20'
Sep 2nd 1764
5h 20min 47s
80° 11' 42
34° 8' 6"B
0° 9'
Sep 2nd 1764
5h 37min 1s
84° 15' 12
32° 11' 51"B
0° 9'
Cluster of small stars, little distant from the previous, on the parallel of F of the Charioteer; the stars are very small, very close & contain nebulosity; with a simple refractor of 3 feet & a half, the stars are barely visible: this cluster is reported on the Chart of the second Comet of 1771, Mem. Acad. 1777. Sep 25th 1764
5h 12min 41s
78° 10' 12
36° 11' 51"B
0° 15'
Cluster of faint stars in the Charioteer, near the star V, at small distance from the two previous clusters; this one is of a square shape & does not contain any nebulosity, if examined with care in a good instrument. Its extent may be 15 minutes of a degree. 39
Oct 24th 1764
21h 23min 49s
320° 57' 10
47° 25' 0"B
1° 0'
Cluster of stars near the tail of the Swan; they can be seen with a simple refractor of 3 feet & a half. 40
Oct 24th 1764
12h 11min 2s
182° 45' 30
59° 23' 50"B
Two stars very near each other & very small, placed at the onset of the tail of the great Bear: they are barely distinguished with a simple refractor of 6 feet. These two stars have been observed while searching for the nebula placed above the back of the great Bear, reported in the book on the shape of celestial bodies, which must have been in 1660, 183d 32' 41" of right ascension, & 60d 20' 33" of north declination, which M. Messier could not see. 41
33
88° 40' 9"
Cluster of stars in the Charioteer, near the star I: with a simple refractor of 3 feet & a half the stars are barely discerned, the cluster does not contain any nebulosity. Its position determined with I.
38 31
5h 54min 41s
Cluster of very small stars, near the left foot of Castor, at little distance from the stars P & K of this constellation. M. Messier reported its position on the Chart of the Comet of 1770. Mem. Acad. 1771, pl. VII. Reported in the English Atlas.
37 st
rd
Aug 30th1764
20h 15min 38s 303° 54' 29" 37° 11' 57"B
Cluster of seven or eight very small stars, which are below J of the Swan, which are seen with a simple refractor of 3 feet & a half in the form of a nebula. Its position is determined with J of the Swan. This cluster is reported on the Chart of the Comet of 1779. 30
35
Jan 16th 1765
6h 35min 53s
98° 58' 12"
20° 33' 0"A
Cluster of stars below Sirius, near U of the great Dog; this cluster appears nebulous with a simple refractor of one foot: but it is only a cluster of small stars. 42
Mar 4th 1769
5h 23min 59s
80° 59' 40"
5° 34' 6"A
Position of the beautiful nebula of the sword of Orion, with the star T which is contained there with three other smaller stars which cannot be seen except in good instruments. M. Messier went into great detail on this great nebula; he has given a drawing of it, made with the most care, which can be seen in the Memoirs of the Academy, year 1771, plate VIII. It was Huyghens who discovered it in 1656: it was since then observed by a large number of astronomers. Reported in the English Atlas.
43
Mar 4, 1769
5h 24min 12s
81° 3' 0"
5° 26' 37"A
Position of the small star which is surrounded by nebulosity & which is below the nebula in the sword of Orion. M. Messier reported it on the drawing of the great one. 44
Mar 4, 1769
8h 7min 22s
126° 50' 30" 20° 31' 38"B
Cluster of stars known by the name of the nebulae of Cancer, the reported position is that of star C. 45
Mar 4, 1769
3h 33min 48s
53° 27' 4"
which appeared in the volume of the Academy on the same year 1779. Re-observed on April 10th 1781. 50
End of the printed catalog by M. Messier.
Those that follow have been observed by M. Messier, after the printing of his memoir. 7h 31min 11s
112° 47' 43"
14° 19' 7"A
Cluster of very small stars, between the head of the great Dog & the two hindlegs of the Unicorn, determined by comparing this cluster with the 2nd star of the Ship, 6th magnitude, according to Flamsteed; the stars are not visible except in a good refractor; this cluster contains a bit of nebulosity. 47
Feb 19th 1771
7h 44min 16s
116° 3' 58"
14° 50' 8"A
Cluster of stars little distant from the prev. the stars larger, the middle of the cluster compared with the same star, the second of the Ship. The cluster does not contain any nebulosity.
51
Feb 19th 1771
8h 2min 24s
120° 36' 0"
1° 16' 42"A
Cluster of very small stars, without nebulosity; this cluster is at a little distance from three stars which are at the onset of the tail of the Unicorn. Feb 19th 1771
12h 17min 48s 184° 26' 58" 9° 16' 9"B
Nebula discovered near the starG of the Virgin. It is not without difficulty that this nebula can be seen in a simple refractor of 3 feet & a half. The Comet of 1779 was compared to this nebula by M. Messier on April 22nd & 23rd: the Comet & the Nebula had the same brightness. M. Messier reported this nebula on the Chart of the path of this Comet,
13h 20min 23s 200° 5' 48"
48° 24' 24"B
Sep 7th 1774
23h 14min 38s 348° 39' 27" 60° 22' 12"B
Cluster of very small stars, mingled with nebulosity, which cannot be seen except in an achromatic refractor. While observing the Comet which appeared in that year, M. Messier saw this cluster, which had been near the Comet on September 7th 1774: it is below the star d of Cassiopeia: this star d served to determine the star cluster & the Comet. 53
Feb 26th 1777
13h 2min 2s
195° 30' 26" 19° 22' 44"B
Nebula without stars, discovered below & near the hair of Berenice, at a little distance from the 42nd star of this constellation, according to Flamsteed. This nebula is round & conspicuous. The Comet of 1779 was compared directly to this nebula, & M. Messier reported it on the Chart of this Comet, which will be included in the volume of the Academy for 1779. Re-observed on April 13th 1781: it resembles the nebula which is above the Hare. Jul 24th 1778
18h 40min 52s 280° 12' 55" 30° 44' 1"A
Very faint nebula, discovered in the Archer; its center is brilliant & does not contain any star, as seen with an achromatic refractor of 3 feet ½. Its position was determined with ] of the Archer 3rd magnitude. 55
49
Jan 11th 1774
Very faint nebula, without stars, near the ear of the southern of the Greyhounds, below the star K of 2nd magnitude of the tail of the Great Bear: M. Messier discovered this nebula on October 13th 1773, while observing the Comet which appeared in this year. One cannot see it but difficultly with a simple refractor of 3 feet ½: near it is a star of 8th magnitude. M. Messier reported its position on the Chart of the Comet observed in 1773 & 1774. Memoirs of the Academy 1774, plate III. It is double, each one with a brilliant center, separated from each other 4' 35". The two atmospheres touch each other. One is fainter than the other. Re-observed several times.
54 48
102° 57' 28" 7° 57' 42"A
Cluster of small stars more or less brilliant, below the right thigh of the Unicorn, above the star T of the ear of the great Dog, & near a star of 7th magnitude. M. Messier observed this cluster while observing the Comet of 1772. It is reported on the Chart of this Comet, on which it is traced. Mem. Acad. 1772.
52
Feb 19th 1771
6h 51min 50s
23° 22' 41"B
Cluster of stars, known by the name of the Pleiades. The reported position is that of the star Alcyone.
46
Apr 5th 1772
Jul 24th 1778
19h 26min 2s
291° 30' 25" 31° 26' 27"A
Nebula that is a whitish patch, about 6 minutes in extent, the light is even & appears not to contain any star. Its position was determined with ] of the Archer, by means of an intermediate star of 7th magnitude. This nebula was discovered by M. Abbé de la Caille. Mem. Acad. 1755, p. 194. M. Messier had searched for it without success on July 29th 1764, as reported in his Memoir.
43
56
Jan 23rd 1779
19h 8min 0s
287° 0' 1"
29° 48' 14"B
Nebula without star, having little light; M. Messier discovered it on the same day as the discovery of the Comet of 1779 on January nineteenth. On the 23rd, he determined its position by comparing it to the star No. 2 of the Swan, according to Flamsteed: it is near the milky way, near to it is a star of 10th magnitude. M. Messier reported it on the Chart of the Comet of 1779. 57
Jan 31st 1779
18h 45min 21s
281° 20' 8"
32° 46' 3"B
Mass of light placed between J & E of the Lyre, discovered while observing the Comet of 1779, which passed nearby: it seems that this mass of light, which is rounded, is composed of very small stars: with the best telescopes it is not possible to perceive them, there is only a suspicion left that they are there. M. Messier reported this mass of light on the Chart of the Comet of 1779. M. Darquier, in Toulouse, discovered this nebula, while observing the same Comet, & and he reports: “Nebula between J & E of the Lyre; it is quite lacklustre, but perfectly terminated; it is large as Jupiter & resembles a fading Planet.”
determined the position but approximately. Re-observed on March 22nd 1781. 63
58
Apr 15 1779
h
12 26
min
30
s
186° 37' 23" 13° 2' 42"B
Very faint nebula discovered in the Virgin, near the parallel of H 3rd magnitude. The least light to illuminate the micrometer wires causes it to disappear. M. Messier reported it on the Chart of the Comet of 1779, which can be found in the volume of the Academy of the same year. 59
Apr 15th 1779
12h 30min 47s 187° 41' 38" 12° 52' 36"B
Nebula in the Virgin & in the neighborhood of the previous, on the parallel of H, which served for the determination: it is of the same light as that above, just as faint. M. Messier reported it on the Chart of the Comet of 1779. 60
Sep 15th 1779
12h 32min 28s 188° 6' 53"
12° 46' 2"B
Nebula in the Virgin, a little bit more apparent than the two previous ones, likewise on the parallel of H, which has served for the determination. M. Messier reported it on the Chart of the Comet of 1779. He discovered these three nebulae while observing this Comet which passed very near to them. The latter passed very near on April 13th & 14th, that being both in the field of the refractor, he could not see it; it was not until the 15th, while searching for the Comet, that he saw this nebula. These three nebulae do not appear to contain any star. 61
May 11th 1779
12h 10min 44s
182° 41' 5"
5° 42' 5"B
Very faint nebula & difficult to perceive. M. Messier took this nebula for the Comet of 1779 on May 5th, 6th & 11th; on the 11th he recognized that this was not the Comet; but a nebula which was found on its path & at the same point in the Sky. 62
June 4th 1779
16h 47min 14s 251° 48' 24" 29° 45' 30"A
Very fine nebula, discovered in the Scorpion, it resembles a small Comet, its center is brilliant & surrounded by a faint light. Its position was determined by comparing it to the star W of the Scorpion. M. Messier had already seen this nebula on June 7th 1771, without having
44
13h 4min 22s
196° 5' 30"
43° 12' 37"B
Nebula discovered by M. Méchain in the Hunting Dogs. M. Messier located it; it is faint, it has about the same brightness as the nebula reported under No. 59: it does not contain any star, & the least light to illuminate the wires of the micrometer causes it to disappear: there is a star of 8th magnitude near it, which precedes the nebula on the hour wire. M. Messier reported its position on the Chart of the path of the Comet of 1779. 64
Mar 1st 1780
12h 45min 51s
191° 27' 38" 22° 52' 31"B
Nebula discovered in the hair of Berenice, which is half as apparent as that one which is below the hair. M. Messier reported its position on the Chart of the Comet of 1779. Re-observed on March seventeenth 1781. 65
th
June 14th 1779
Mar 1st 1780
11h 7min 24s
166° 50' 54" 14° 16' 8"B
Nebula discovered in the Lion; it is very faint & does not contain any star. 66
Mar 1st 1780
11h 8min 47s
167° 11' 39"
14° 12' 21"B
Nebula discovered in the Lion; its light very faint & very near the previous: they appear both in the same field of the refractor. The Comet observed in 1773 & 1774 had passed between these two nebulae from November 1st to 2nd 1773. M. Messier did not see them then, without doubt, because of the light of the Comet. 67
Apr 6th 1780
8h 36min 28s
129° 6' 57"
12° 36' 38"B
Cluster of small stars with nebulosity, below the southern Claw of the Crab. The position determined with the star D. 68
Apr 9th 1780
12h 27min 38s 186° 54' 33" 25° 30' 20"A
Nebula without stars below the Raven & the Hydra; it is very faint, very difficult to perceive with the refractors; near it is a star of the sixth magnitude.
Extension of the Catalog of Nebulae & Star Clusters of M. Messier, included in the Connoiss. des Temps for 1783, page 225, & year 1784, page 255 & following. 69
Aug 31st 1780
18h 16min 47s
274° 11' 46"
32° 31' 45"A
0° 2'
Nebula without stars, in the Archer, below his left arm & near the arc; near it is a star of 9th magnitude: its light is very faint, one cannot see it but in good weather, & the least light employed to illuminate the wires of the micrometer causes it to disappear: its position was determined by H of the Archer: this nebula was observed by M. de la Caille, & reported in his catalog; it resembles the nucleus of a small Comet. 70
Aug. 31st 1780
18h 28min 53s
277° 13' 16"
32° 31' 7"A
0° 2'
Nebula without star, near the previous, & on the same parallel: near it is a star of the ninth magnitude & four small telescopic stars, nearly on a straight line, very near each other, & are placed above the nebula, as seen in an inverting refractor; the nebula determined by the same star H of the Archer. 71
Oct 4th 1780
19h 43min 57s
M. Méchain
295° 59' 9"
18° 13' 0"B
296° 0' 4"
18° 14' 21"
0° 3 ½'
Nebula discovered by M. Méchain on June 28th 1780, between the stars J & G of the Arrow. On the following October 4th, M. Messier located it: its light is very faint & does not contain any star; the least light causes it to disappear. It is placed about 4 degrees below that which was discovered by M. Messier in the Fox. See No. 27. He reported it on the Chart of the Comet of 1779. 72
Oct 4th 1780
20h 41min 23s
M. Méchain
310° 20' 49"
13° 20' 51"A
310° 21' 10"
13° 21' 24" th
Oct 4th & 5th 1780 20h 46min 52s
311° 43' 4"
Oct 18th 1780 M. Méchain
1h 24min 57s
M. Méchain
76
13° 28' 40"A
21° 14' 9"
14° 39' 35"B 14° 36' 0"
Oct 21st 1780
1h 28min 43s
M. Méchain
298° 17' 24"
22° 32' 23"A
298° 17' 30"
22° 32' 0"
22° 10' 47"
50° 28' 48"B
22° 10' 26"
50° 28' 12"
0° 2'
Nebula on the foot of Andromeda, seen by M. Méchain on Sept. 5th 1780, & of which he reports: “This nebula does not contain stars; it is small & faint.” On the following October 21st M. Messier located it with his achromatic refractor, & it seemed to him that it was composed of nothing but very small stars, which contained nebulosity, & the least light employed to illuminate the wires of the micrometer caused them to disappear: the position determined with the star I of Andromeda, fourth magnitude. 77
Dec 17th 1780
2h 31min 30s
M. Méchain
37° 52' 33"
0° 57' 43"A
37° 52' 58"
0° 57' 44"
Cluster of small stars, which contain nebulosity, in the Whale, & on the parallel of the star G reportedly of third magnitude, & which M. Messier estimated to be only of the fifth. M. Méchain saw this cluster on October 29th 1780 in the form of a nebula. 78
21° 17' 0"
19h 53min 10s
Nebula without star, between the Archer & the head of the Capricorn: seen by M. Méchain on August 27th & 28th 1780. M. Messier located it on October 5th following & on the eighteenth compared it with the star No. 4, sixth magnitude of the Capricorn, according to Flamsteed: it appears to M. Messier that it is composed only of very small stars, containing nebulosity: M. Méchain reported it as nebula without stars. M. Messier saw it on October 5th; but the Moon was on the horizon, & it was not until the eighteenth of the same month that he was able to judge its appearance & determine its position.
th
Cluster of three or four small stars, which resemble a nebula at first glance, contains a bit of nebulosity: this cluster is placed on the parallel of the previous nebula: its position was determined by the same star Q of the Water-Bearer. 74
Oct 18th 1780
0° 2'
Nebula seen by M. Méchain the night of August 29 to 30 1780, above the neck of the Capricorn. M. Messier located it on October 4th & 5th following: its light faint as the previous; near it is a small telescopic star: its position determined with the star Q of the Water-Bearer, fifth magnitude. 73
75
Nebula without star, near the star K of the Link of the Fishes, seen by M. Méchain at the end of September 1780, & and of which he reports: “This nebula does not contain stars; it is quite large, very obscure, extremely difficult to observe, one can determine it more exactly in good frosts.” M. Messier located it & found it, as M. Méchain described it: it was compared directly with the star K of the Fishes.
Dec 17th 1780
5h 35min 34s
M. Méchain
83° 53' 35"
0° 1' 23"A
83° 53' 2"
0° 0' 31"
0° 3'
Cluster of stars, with much nebulosity in Orion & on the parallel of the star G of the Belt, which served in determining its position; the cluster follows the star on the hour wire by 3d 41' & the cluster above the star by 27' 7". M. Méchain has seen this cluster in the beginning of 1780, & reports hence: “On the left side of Orion, 2 to 3 minutes of diameter, there are two fairly brilliant nuclei, surrounded by nebulosity.” 79
Dec 17th 1780
5h 15min 16s
M. Méchain
78° 49' 2"
24° 42' 57"A
78° 47' 10"
24° 44' 46"
Nebula without star, placed below the Hare, & on the parallel of a star of the sixth magnitude: seen by M. Méchain on October 26th 1780. M. Messier located it on December seventeenth following: this nebula is fine; the center brilliant, the nebulosity little diffuse: its position determined by the star H of the Hare, fourth magnitude. 80
Jan 4th 1781 M. Méchain
16h 4min 0s
240° 59' 48"
22° 25' 13"A
241° 0' 26"
22° 27' 58"
0° 2'
Nebula without star, in the Scorpion, between the stars J & G, compared with J to determine its position: this nebula is round, the center brilliant & resembles the nucleus of a small Comet, surrounded by nebulosity. M. Méchain saw it on January 27th 1781.
45
81
Feb 9th 1781
9h 37min 51s
M. Méchain
144° 27' 44" 70° 7' 24"B 144° 27' 0" 70° 4' 0"
Nebula near the ear of the great Bear, on the parallel of the star d, of the fourth to the fifth magnitude: its position determined with this star. This nebula is slightly oval, the center clear, & it can be seen very well with a simple refractor of three feet & a half. It was discovered at Berlin, by M. Bode, on December 31st 1774, & by M. Méchain, in the month August of 1779.
nebula in the field of the refractor. Its light is one of the faintest & resembles that reported in the Virgin, No. 58. 89
82
Feb 9 1781
h
9 37
min
57
s
M. Méchain
144° 29' 22" 70° 44' 27"B 144° 28' 13" 70° 43' 5"
Nebula without star, near the previous; both appear in the field of the refractor at the same time, this one less apparent than the previous, its light is faint & elongated: at its extremity is a telescopic star. Seen at Berlin, by M. Bode, on December 31st 1774, & by M. Méchain, in the month August of 1779. 83
Feb 17th 1781
13h 24min 33s 201° 8' 13"
28° 42' 27"A
Nebula without star, near the head of the Centaur: it appears as a faint & even light, but so difficult to observe, that the least light to illuminate the wires of the micrometer causes it to disappear. It is only with much attention that it can be seen: it forms a triangle with two stars estimated of the sixth and seventh magnitude: determined with the stars l, i, k, h, of the head of the Centaur: M. de la Caille had already determined this nebula. See at the end of this Catalog. 84
Mar 18th 1781
12h 14min 1s
183° 30' 21" 14° 7' 1"B
Nebula without star, in the Virgin; its center is rather bright, surrounded by a light nebulosity: its brightness & its appearance resemble those of this Catalog, Nos. 59 & 60. 85
Mar 18th 1781
12h 14min 21s
M. Méchain
183° 35' 21" 19° 24' 26"B
12h 15min 5s
91
Mar 18th 1781
12h 19min 48s 184° 57' 6"
13° 38' 1"B
Nebula without star, in the Virgin, below & quite near of a star of eighth magnitude, the star having the same right ascension as the nebula, & its declination is 13d 42' 21" north. This nebula appears of the same brightness as the two nebulae Nos. 84 & 86. 88
Mar 18th 1781
12h 21min 3s
185° 15' 49" 15° 37' 51"B
Nebula without star, in the Virgin, between two small stars & and one star of the sixth magnitude, which appear at the same time as the
46
12h 25min 48s 186° 27' 0"
14° 22' 50"B
Mar 18th 1781
12h 26min 28s 186° 37' 0"
14° 57' 6"B
Nebula without star, in the Virgin, above the previous No. 90: its light is still fainter than those above. Note. The constellation of the Virgin, & especially its northern wing, is one of the constellations which encloses many Nebulae: this Catalogue contains 13 of them determined: namely, the Nos. 49, 58, 59, 60, 61, 84, 85, 86, 87, 88, 89, 90 & 91. All these nebulae appear without stars: they cannot be seen except in a very good sky, & near their passages of the Meridian. The majority of these nebulae were indicated to me by M. Méchain. 92
Mar 18th 1781
17h 10min 32s
257° 38' 3"
43° 21' 59"B
0° 5'
Nebula, fine, conspicuous, & of a great brightness, between the knee & the left leg of Hercules, seen very well with a refractor of one foot. It does not contain any star; the center is clear & brilliant, surrounded by nebulosity & resembles the nucleus of a big Comet: its light, its magnitude, come very near to that of the nebula which is in the girdle of Hercules. See No. 13 of this Catalog: its position was determined by comparing it directly to the star R of Hercules, fourth magnitude: the nebula & star on the same parallel. 93
Mar 20th 1781
7h 35min 14s
113° 48' 35"
23° 19' 45"A
0° 8'
Cluster of small stars, without nebulosity, between the great Dog & the prow of the Ship.
183° 46' 21" 14° 9' 52"B
Nebula without star, in the Virgin, on the parallel & very near of the nebula above, No. 84: their appearance is the same, & both appear the same field of the refractor. 87
Mar 18th 1781
Nebula without star, in the Virgin: its light as faint as the previous, No. 89.
94 Mar 18th 1781
13° 46' 49"B
183° 35' 45" 19° 23' 0"
Nebula without star, above & near the spike of the Virgin, between the two stars of the hair of Berenice, Nos. 11 & 14 of Flamsteed’s Catalog: this nebula is very faint. M. Méchain determined its position on March 4th 1781. 86
12h 24min 38s 186° 9' 36"
Nebula without star, in the Virgin, at a little distance from & on the same parallel as the nebula reported above, No. 87. Its light was extremely faint & rare & it is not without trouble that it can be perceived. 90
th
Mar 18th 1781
Mar 24th 1781
12h 40min 43s 190° 10' 46" 42° 18' 43"B
M. Méchain
0° 2 ½'
190° 9' 38" 42° 18' 50"
Nebula without star, above the heart of Charles, on the parallel of the star No. 8, sixth magnitude, of the Greyhounds, according to Flamsteed: its center is brilliant & the nebulosity slightly diffuse. It resembles the nebula which is below the Hare, No. 79: but this one is finer & more brilliant; M. Méchain did discover it on March 22nd 1781. 95
Mar 24th 1781 M. Méchain
10h 32min 12s
158° 3' 5"
12° 50' 21"B
158° 6' 23"
12° 49' 50"
Nebula without star, in the Lion, above the star l: its light is very faint.
96
Mar 24th 1781
10h 35min 5s
M. Méchain
By M. Méchain, which M. Messier has not yet seen.
158° 46' 20" 12° 58' 9"B 158° 48' 0" 12° 57' 33"
Nebula without star, in the Lion, near the previous; this one is less apparent, both on the parallel of Regulus: they resemble the two nebulae in the Virgin, Nos. 84 & 86. M. Méchain saw both on March twentieth 1781. 97
Mar 24th 1781
11h 1min 15s
165° 18' 40" 56° 13' 30"A
0° 2'
Nebula in the great Bear, near E: it is difficult to observe, reports M. Méchain, especially when illuminating the wires of the micrometer: its light is faint, without star. M. Méchain saw it for the first time on February 16th 1781, & the position is given according to him. Near this nebula he has seen another, which has not been determined yet, also a third one which is near to J of the great Bear. 98
Apr 13th 1781
12h 3min 23s
101 Mar 27th 1781
13h 43min 28s 208° 52' 4"
55° 24' 25"B
0° 7'
Nebula without star, very obscure & pretty large, 6 to 7 minutes in diameter, between the left hand of the Herdsman & the tail of the great Bear. It can be barely distinguished when the wires are lit. 102
Nebula between the stars R of the Herdsman & L of the Dragon: it is very faint; near it is a star of the sixth magnitude. 103
Cluster of stars between H and G of the leg of Cassiopeia.
180° 50' 49" 16° 8' 15"B
Nebula without star, of an extremely faint light, above the northern side of the Virgin, on the parallel & near the star No. 6, fifth magnitude, according to Flamsteed. M. Méchain saw it on March 15th 1781. 99
Apr 13th 1781
12h 7min 41s
181° 55' 19" 15° 37' 12"B
Nebula without star, of a very rare light, but a little bit more clear than the previous, placed on the northern side of the Virgin, & near the same star, No. 6, of the hair of Berenice. The nebula is between two stars of the seventh & eighth magnitude. M. Méchain observed it on March 15th 1781. 100 Apr 13th 1781
12h 11min 57s
182° 59' 19" 16° 59' 21"B
Nebula without star, of the same brightness as the previous, placed in the spike of the Virgin. Seen by M. Méchain on March 15th 1781. These three nebulae, Nos. 98, 99 & 100, are very difficult to distinguish, because of the faintness of their light: they cannot be seen except in good weather, & near their passages of the Meridian.
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Remarks on Messier’s catalog Messier’s catalog is, by no means, a uniform series of observations. The descriptions stem from the use of different telescopes (see box) and are, consequently, of varying quality. The object brightness, which Messier would still see or describe as faint, varies accordingly. The faintest object of the first catalog version is also its first, M 1 with magnitude 8.4. Almost all other entries are brighter than 8th magnitude, most fall even into the range of 5th to 7th magnitude. Apart from M 31, M 32, and M 33, no galaxies are listed in the first catalog version; they were too faint for Messier’s instrumentation at that time. Hence, most of the first 45 entries are open clusters, some globular clusters and a few galactic nebulae, plus one single planetary nebula. For his second catalog, Messier was able to use better optical instruments. By 1773 he had received one of the first achromatic refractors from the collection of his friend de Saron. This telescope is mentioned in detail in the description of Messier’s drawing of M 42. From then on, Messier’s discoveries reach nearly down to magnitude 10, including many galaxies. This trend continues with the third part, which includes objects at the perception limit of a modern 2-inch telescope under a dark sky. Many of these were contributed by Méchain, who worked at the Royal Observatory – we may safely assume that his instruments were better than Messier’s. Messier’s first catalog (M 1 to M 45) contains exact descriptions of the telescopes and magnifications he used. The telescope mentioned in almost every more detailed description is a Gregorian reflector of 30 inches (French) focal length, 6 inches aperture and a (probably fixed) magnification of 104×. Modern notation would have it as a 6.4-inch f/5 system (162mm aperture, 810mm focal length) with an eyepiece focal length of 7.8mm. With an apparent field of view of 30°, it covered 17' in the sky. This telescope is mentioned in the descriptions of M 2, 3, 5, 9, 10, 11, 15, 19, 22, 26, 27, 28, 30, 31, 35, 42, and 43, while for M 13 and M 31, a Newtonian telescope of 4.5-feet focal length and a power of 65× is noted. It is most likely that Messier made his discoveries with smaller telescopes, which he used for comet hunting. The purpose of the larger optics was to make detailed descriptions and to measure the positions of the new objects. In the third catalog, Messier ranks his telescopes according to their focal length in five categories. These were also used by him to characterize the difficulty of an object:
A page from Messier’s observing logbook. In his entry made on the 7th of July 1758, Messier describes the reflector with which he observed the moons of Jupiter and stellar occultations. As shown here, the telescope is set up for measurements of the exact eyepiece focal length.
1 foot observed objects: M 3, M 5, M 13, M 33, M 41, M 92
2 foot The faintest of these targets is M 92 at magnitude 6.4. M 41 was not recognized by Messier as a star cluster but taken for a nebula. Since its brightest stars reach magnitude 6.9, the limiting magnitude of this telescope under the Parisian night sky must have been between magnitudes 6.5 and 7.0.
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observed objects: M 2 The optical performance of this telescope cannot have been much better than that of the 1-foot telescope.
3 foot observed objects: M 8, M 10, M 11, M 25, M 26, M 30, M 34, M 35 The faintest of these objects is M 26 with magnitude 8.0. However, M 10 at magnitude 6.6 was already characterized as “difficult” by Messier, and resolving the stars of M 25 beginning at magnitude 6.7 was not easy for him, either. He barely resolved M 34 (brightest stars magnitude 7.3), but not M 11 (brightest stars magnitude 8) which he described as a nebula when seen with this instrument, likewise with M 35, which Messier could resolve only with the Gregorian telescope. Hence, the limiting magnitude of the 3-foot refractor must have been between magnitudes 7.5 and 8.0.
3.5 foot observed objects: M 14, M 17, M 18, M 19, M 22, M 23, M 26, M 27, M 28, M 29, M 30, M 32, M 36, M 37, M 39, M 49, M 51, M 81 The faintest of these objects is the Virgo cluster galaxy M 49 at magnitude 8.4. Like M 28, M 30, and M 51, it appeared “very faint” to Messier. Some star clusters remained unresolved: M 18 (brightest stars magnitude 8.7), M 29 (brightest stars 8.6), M 36 (brightest stars 8.7), and M 37 (brightest stars 9.2). This indicates a limiting magnitude of 8.5.
6 foot The only time Messier mentions this focal length is in connection with M 40. He described this stellar pair of magnitudes 9.0 and 9.3 as nebulous, and we may infer a limiting magnitude of around 10.0 from that. For the remaining objects, Messier did not specify which telescopes were used. These include many of the entries in the third version of the catalog. However, it is likely that Messier chiefly employed the 3.5-inch f/12 achromatic refractor (89mm aperture, 1067mm focal length), which he had received from de Saron and described as his favorite instrument. This telescope was mentioned without full details several times, for example in the descriptions for M 54 (observed 1778) and M 76. One criterion Messier used to describe an object as faint was its inability to be seen even when the micrometer’s illumination was set at its lowest level. In this category we find M 58, 59, 63, 69, 71, 76, 83, 88, 89, 90, 91, 97, 98, 99, and M 100, all observed after 1779. The faintest of these are M 76, M 98, and M 91 at magnitude 10.1. Messier could resolve the brightest stars in the clusters M 4 (magnitude 10.8), M 46 (brightest stars 8.7), M 52 (brightest stars 8.2), and M 67 (brightest stars 9.7). But M 71 (brightest stars magnitude 12.1) and other globular clusters remained a “nebula without stars.” Hence, the telescopic limiting magnitude must have been about 11.0 for the 6.4-inch Gregorian he used in the first edition, as well as for the 3.5-inch Dollond he prefered later. Modern visual observers are puzzled by the lack of observed detail reported by Messier. The only globular cluster in which he was able to see the brightest stars was M 4 – the rest remained a “nebula without stars” to him. By contrast, a modern 3.5-inch refractor under dark skies would resolve the brightest stars in at least half a dozen of Messier’s globular clusters. Furthermore, it appears that Messier had not seen any of the true nebulosity of M 20, and he probably mistook M 76 and M 78 for star clusters. He even believed that he saw stars in M 57, which had been described correctly as a nebulous disk by its discoverer Darquier already. Méchain, in particular, seems to have carried out better observations than Messier in that respect. Good examples are their different descriptions of the four objects M 75 to M 78, in which Messier disagrees with Méchain’s notes:
Why were some showpieces left out by Messier? The Messier catalog includes most of the finest showpieces in the night sky, but a few were left out. Since these missing objects were easily within reach of Messier’s telescopes, many deep-sky observers have been puzzled about their omission. The reason is simple: Messier was not interested in deep-sky objects for their own sake. Instead, he did not want to confuse them with comets. He did not look for them in a systematic way, not even during those few months of intensive searching. That separates him from William Herschel, who started to work on his impressive catalog in 1782. But considering the often accidental findings of Messier, his catalog is rather surprisingly complete. The puzzling question in this context is: why then did Messier add four well-known spectacular objects, M 42 to M 45, to his initial list of 41? Certainly, these were not to be confused with a comet. Probably, in this one instance, Messier was tempted to round up his list to a number larger than the 42 objects of his role-model Lacaille. But at the same time, there were not enough showpieces to make it to the next round number, 50 – so he left some out. The most prominent example is the double cluster h & Fin Messier’s days known as F Per. Messier must have known it, and his contemporary Bode described its field as “to the north of the star F a lot of small stars, looks nice in telescopes.” The fact that this object already had a proper designation and was shown by all star-charts may have been the very reason why Messier did not include it in his list. Several other bright objects were just too large for the field of view of Messier’s telescopes. Good examples are the widely spread star clusters IC 4665 or the “coat-hanger,” Collinder 399, which would not have been obvious through Messier’s eyepiece. Messier also knew of some objects in the southern sky, but he wanted a catalog of objects that are all observable from Paris, and which he had observed in person. And it is this last of his principles that made his catalog stand out in quality from the lists of his contemporaries. The resulting low number of errors in Messier’s list also made his catalog successful.
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Messier’s telescopes Which telescopes did Messier use to discover and to observe his 110 objects? The answer is not easy to give, for three reasons: firstly, hardly any sources have survived which would describe the contemporary instrumentation of the observatory at the Hôtel de Cluny. Secondly, Messier used a variety of telescopes of five different categories, as we know from his descriptions. And thirdly, with the gradual availability of achromatic lenses, there was a tremendous change in optical telescope quality around the time the catalog was accomplished. In the seventeenth century, telescopes with chromatic lenses (i.e., refractors without colorcorrection) were the standard. They had a single objective lens and an eyepiece made of two lenses. The construction principles had been optimized by Christian Huygens. In order to keep the chromatic aberration of the objective lens within limits, these refractors had to have extremely long focal lengths: an aperture of 70mm required a length of 8m! Therefore, the telescopes were made of two movable parts, both riding on a long rod. With the longest telescopes, they were connected only by a rope under tension. The objective lens was at the far upper end, mounted on a high pole or stepladder by means of a simple ball-head. The eyepiece at the lower end by the observer resided on a small stepladder. Equatorial mounts were not yet known, and a tube would have been too heavy for these long telescopes. The long focal lengths imposed magnifications of over 100× and very small fields of view. In our time, it is hard to imagine how cumbersome any telescopic observation must have been in those days. First, the object had to be carefully aimed at with the rod. Then, with a most gentle touch, the remote ball-head, supporting the objective lens at the far end, had to be fixed. Tracking the object with this clumsy construction and a magnification of over 100× must have required a lot of training and patience. Despite such disadvantages, all major astronomical discoveries between 1650 and 1730 had been achieved with this kind of chromatic refractor, and even whole maps of the moon had been drawn!
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We can be pretty certain that Messier’s “ordinary refractors” of 1, 2, 3, 3.5, and 6-foot focal length were exactly that kind of clumsy, chromatic telescope. He favored the smaller telescopes with focal lengths of 1 meter or less, because these had a tube which reduced stray light and greatly facilitated their use. But even Messier’s 6-foot refractor was a dwarf compared to the longest contemporary refractors with focal lengths of over 30m. Around the mid-eighteenth century, coinciding with Messier’s active period, the time of these monstrous telescopes finally came to an end as the result of two new developments: first, James Short (1710–1768), a London-based optiContemporary impression of a tubeless chromatic cian, developed a method to produrefractor in the seventeenth century. The objective ce telescope primary mirrors from (i) is mounted and counterbalanced (k–l) on a shiny metal-alloys (front-silvered ball-head (m). It is connected with the eyepiece glass-mirrors would come only la(o) by a rope under tension. This cumbersome ter). From 1743 to 1768, Short was construction was dictated by the long focal length the first to produce telescopes in of the single objective lens, required to keep the large numbers. 1400 Short-reflecchromatic aberration as small as possible. tors were made by his little company, mostly employing the Gregorian design and mounted on a short table-top stand or ordinary tripod. many years before he could lay his hand on For quite some time, Short’s reflectors were one of these fine telescopes – which was not regarded as the best telescopes worldwide. His until his rich friend de Saron gave him one. largest mirrors would reach 22 inches diameIn 1772, Dollond’s patent rights expired, and ter! in the face of new competition, the prices for The second important invention was made his telescopes dropped considerably. Still, for only a little later, also in London: the achromany years Dollond’s company remained the matic (color-corrected) refractor. The idea of most important producer of achromatic recombining lenses from two different types of fractors – a technical term, by the way, which glass to minimize the color aberration already was coined by John Bevis, the discoverer of existed, but it was the optician John Dollond M 1. (1706–1761), who secured the patent rights In the 1807 edition of the Connaissance des and started large-scale production of achroTemps, Messier published a list of telescopes matic refractors in 1758. After his death, his he had used in the years 1765 to 1769, in son took over and expanded the company. his work on the first catalog of 45 objects. In the beginning, Dollond’s refractors were However, their specifications almost excluvery expensive, due to extraordinary desively refer to the focal lengths, given in the mand. Hence, working in an observatory with French foot (slightly larger than the respechumble financial means, Messier had to wait tive English units: 1 French foot = 0.3248 m
= 12 French inch, 1 French inch = 2.7cm), rarely to the aperture. However, from that source, and from a few more remarks in the literature, we know at least some of the telescopes available to Messier: 1) Chromatic refractors of short focal length (“lunettes ordinaires” or “ordinary refractors”) and, possibly, draw-tube telescopes with erect images. The focal lengths were between 1 foot and 3.5 feet, none of the apertures were more than 3.5 inches (80mm), and their optical performance scarcely reached that of modern Dollond refractors, the first achromatic refractors binoculars. produced in large numbers, arrived on the optical 2) Chromatic refractors of market in 1758. Messier used such a telescope long focal length (25 to 30 with 90mm (3.5 inches) of aperture for many of feet or 8.1m to 9.7m), with his deep-sky observations. magnifications of 102× to 138×. These were built according to the principles developed by Huygens, with an f-ratio of over century optics had no coating and, because of 1:100 to keep color aberration under control. their inferior transmission, had a smaller efHence, the respective telescopes at hand for fective aperture by today’s standards. In 1771, Messier would have been between 70/8100 Messier used a low-power (27×) 3.5-feet mm and 80/9740 mm. It was already pointed achromatic refractor for comet observation, out how cumbersome their use was in nightalso given to him by his friend de Saron. For ly practice, providing only a very small field his stay in Lorraine in 1772, he took another of view, and this is why Messier as a comet achromatic refractor from de Saron with him. hunter hardly ever used them. In addition, a It had a focal length of 5 feet, magnified 60×, Campani refractor is mentioned, with a maand was made by the optician Lestang. He gnification of 64× and coming from a sevenalso took an “ordinary [chromatic] refractor” teenth-century optical workshop. It, too, had of 3.5 feet and a possibly achromatic refractor a chromatic lens with very long focal length. of 2 feet (“lunette de nuit”). In the publica3) Achromatic Dollond-refractor with 3¼ tion of a solar observation in 1777, Messier French-foot (1.07 m) focal length and a mareported use of a 3.5-feet achromat with a gnification of 120×. This telescope appears to triplet-lens objective. And in 1781, he mentibe the one which Messier had described as his oned a small achromatic refractor of 405mm favorite instrument, given to him by de Saron. focal length, as well as a “large achromatic It was specified (in English measurements) as refractor on an equatorial machine” – equahaving a 42-inch focal length and 3.5-inch torial mounts would become more common aperture (89/1067mm) and had the same observatory equipment only in the nineteenth magnification of 120×. It is mentioned in the century, after Joseph Fraunhofer invented descriptions of M 54 and M 76. We have to what is known today as the German equatoconsider, however, that the late-eighteenthrial.
Gregorian reflectors made by Short were in widespread use at the end of the eighteenth century. Apart from a large telescope with a 310mm aperture, Messier used a smaller model similar to the one pictured here.
4) Gregorian reflector made by Short with 6-feet (1.95m) focal length and a magnification of 110×. The optical specifications of Short’s telescopes are known very well from his price lists. A telescope of such a focal length had the remarkable aperture of 12 inches. In addition, Messier mentioned a Short reflector of only 1 foot focal length with 44× magnification, which must have had 3 inches of aperture as a Gregorian. The Gregorianreflector he initially used, for the first catalog version, had an 810mm (32-inch) focal length and an aperture of 162mm (6.4 inches). 5) Newtonian reflector of 4.5-feet (1.46m) focal length and a magnification of 60×, with 8 inches of aperture. This telescope belonged to the Royal Observatory, but Messier was allowed to use it occasionally, as for detailed observations of M 42 and Comet Halley.
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• M 75: Messier believed that he saw individual stars, Méchain reported just a nebula. And indeed, at magnitude 14.6, even the brightest individual stars are far below the perception limit of Messier’s and Méchain’s telescopes. • M 76: as above, Messier reported individual stars, Méchain just a nebula, but the object does not contain any stars brighter than 13th magnitude. Messier could not have seen them. • M 77: as above, Messier took it for a star cluster, while Méchain saw a nebula. In fact, it is a galaxy with a star-like core. • M 78: Messier saw a star cluster with nebulosity, Méchain a nebula with two bright cores. In reality, this is a reflection nebula with two embedded 9th-magnitude stars. For some other objects, Messier’s observational impressions are obviously so vague that he was misled in determining the type of object. Some discrepancies are so large that several modern astronomers have started to doubt whether Messier saw the respective objects at all. One is the Trifid Nebula M 20, which was classified by Messier as a star cluster. Another example is the aforementioned M 57, where Messier believed the Ring Nebula consisted of stars. A different case is M 16. Here, Messier correctly reported a star cluster with nebulous background, but the real nebula is too faint to have been seen by him. It was discovered photographically in the early twentieth century and received a separate designation as IC 4703. However, this may well be a misjudgment of Messier’s visual talents. We may simply be underestimating the light pollution of nocturnal Paris in the eighteenth century. In fact, at that time, Paris was the largest city in the world with a population of 800,000. There are contemporary descriptions of how chaotic the situation was in the large city. Smoke from oven-heated houses, numerous factories and open fires must have created air pollution considerably worse than today’s, scattering and absorbing more starlight. In addition, all public streets and squares were floodlit by oil-burning lamps every winter (October to March) from 1667 until their gradual destruction after the French revolution in 1789. Not surprisingly, the Royal Observatory (founded in 1667) was given a location outside the city, but the Observatory of the Navy was quite central. Hence, Messier’s night sky may have been much worse than we imagine. Messier’s notes themselves give an impression of the severity of light pollution in his day. Assuming a loss of transmission due to uncoated optics of 30% in his 3.5-inch Dollond refractor would lead to an equivalent aperture of 3 inches or 75mm. Such an instrument has a limiting magnitude of about 12 under dark rural skies (naked-eye limit 6.5). As analyzed above, the faintest stars Messier could actually see with this instrument were around 11.0, which leads to a naked eye limit of about 5.5 – similar to a severely polluted suburban sky today. Messier’s telescopic limit with the 6.4-inch Gregorian was at about th 11 magnitude, as he could see individual stars in M 4 at 10.8, but not resolve any other globular cluster. We know that the metal mirrors of Messier’s time had a very poor reflectance and losses totalled up to 50%, effectively downsizing the 6.4-inch to a mere 4.5-inch. This instrument would have a limiting magnitude of about 11, if the naked eye limit was only 4.5 – which is equivalent to observing conditions frequently occurring today in large cities.
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Another point to consider is the illumination used by Messier for his star-charts, his notes and his reticle. He had no electric light at his disposal; everything was lit with oil lamps and torches – the thought of which would invoke horror in any visual observer today. So, compared to many modern deep-sky observers, Messier was seriously disadvantaged in terms of instrumentation, and yet he also had to deal with the light pollution many of us experience. With this in mind, we can understand Messier’s mistakes and award him the credit he deserves.
Statistics of the Messier objects When Charles Messier observed the objects that eventually made up his famous catalog, his visual impressions only allowed him to distinguish between “amas d’étoiles” (star clusters) and “nebuleuse” (nebulae). By our modern methods of astrophysics, we can finally classify Messier’s objects according to their physical categories. His catalog contains: • • • • • •
6 Galactic nebulae 28 Open clusters 4 Planetary nebulae 29 Globular clusters 40 Galaxies 3 other objects
In this list, M 8 has been counted as an open (star) cluster, because Messier noted the star cluster as the main object. M 16, of which Messier could not see the surrounding nebulosity, is registered as a star cluster, while the nebula has its separate catalog designation (IC 4703). M 20, regarded by Messier as a star cluster like the other two objects, is classified as a galactic nebula today. But in reality, modern classification is still a bit ad hoc. For example, the galactic nebulae M 17, M 20, and M 42 are best known for their dust-enshrouded, young star clusters in the process of formation, only hidden in visual light. M 45, the Pleiades, is the brightest Messier object with a total magnitude of 1.2. This bright star cluster is visible to the naked eye even under a light-polluted sky. The status of the faintest Messier object is shared by M 76, M 91, and M 98, all at a total magnitude of only 10.1. The largest in angular size of all Messier objects is undoubtedly the Andromeda Galaxy (M 31) at 4° × 1°. Under a very dark, transparent sky, a visual size of as much as 5° has been reported. However, in absolute terms, the galaxy M 101 is the physically largest object of the Messier catalog. With a diameter of 184,000 light-years, it reaches 1½ times the size of our neighbor galaxy M 31 and almost twice the size of our own galaxy. M 31 just happens to be the nearest large spiral galaxy, at only 2.5 million light-years distance, which is what makes it look so large. By contrast, the object with the smallest angular diameter is M 40, a pair of stars separated by only 49", followed by M 73 and M 76 at just 1' in diameter. Planetary nebula M 76 appears to be, if its supposed
distance of 2550 light-years is correct, the physically smallest Messier object with a diameter of 0.7 light-years, while both M 40 and M 73 are not physical objects at all. 69 objects in Messier’s list are members of our own Milky Way and thus relatively near: only 430 light-years separate us from the Pleiades, but we are 78,000 light-years from globular cluster M 75, the farthest galactic Messier object. The 41 extragalactic objects are all galaxies, with one exception: M 54 is a globular cluster of the near dwarf galaxy SagDEG. The most distant Messier object is the galaxy M 109 with considerable 67.5 million light-years – that is 157,000× more distant than M 45! On an age scale, the Messier objects cover an even larger range than their distances do. The youngest object, M 1, was created less than 1000 years ago by a supernova, recorded by historic civilizations in the year 1054. The globular clusters M 69 and M 92 have, by contrast, an age of 12 to 13 thousand million years, almost as old as the whole Universe.
The galactic nebulae Galactic nebulae make up a most diverse category, which includes all of the diverse gaseous and dusty nebulae in our galaxy. The Messier catalog contains several star-forming HII regions, a reflection nebula, and a supernova remnant. HII regions contain mostly hydrogen gas that has a very low density by laboratory standards and is ionized by the ultraviolet (UV) light of nearby hot stars. While cool, neutral hydrogen (HI) remains unobservable in visual light, ionized hydrogen (HII) recombines and emits in the Balmer lines of HD at 656nm, and HE at 486nm. From the traces of heavier elements in these gaseous nebulae, we also receive line emission in visual light from doubly ionized oxygen ([OIII], at 501nm and 496nm) and of singly ionized nitrogen ([NII], at 658nm and 655nm). In order to get any nearby or surrounding hydrogen gas to glow, a star must have a sufficiently energetic ultraviolet radiation field. Hence, HII regions are created only by very hot stars of spectral type O and early B. These short-lived, luminous, and massive stars are found only in young star clusters and star-forming regions, which are surrounded by an HII region – gas that was not consumed by the star formation
53
talog is M 78. Well known but faint are the reflection nebulae around the Pleiades. They do not represent leftover material from the formation of the stars, but rather an unrelated interstellar cloud accidentally passed by the cluster. A rare case consists of the orange nebulae that reflect the light of red supergiant Antares, near M 4 and M 80. A very different type of object is M 1: it is the remnant of a very massive star that was destroyed by a supernova explosion nearly 1000 years ago. Such a catastrophic event is caused by the gravitational collapse of a massive stellar core, following the exhaustion of its nuclear fuel. It leaves behind a chaotically structured shell of material expanding at up to 20,000 km/s, the nebulous supernova remnant, and a super-dense stellar remnant, a neutron star. It is so dense because, during the gravitational collapse, electrons and protons have merged to neutrons, which are now packed as densely as in an atomic nucleus. The enormous reduction in size, in combination with conservation of angular momentum, has, for the M 1 neutron star, led to a super-fast rotation of 33 Members Age times per second. The magnetic field has been compressed 332 100 Myr by a factor of 10 million. Its 1000 500–700 Myr axis is inclined with respect 750 220 Myr to the rotation axis, and as 60 240–480 Myr the intense field lines move >300 0.1 Myr rapidly through the surroun64 80–100 Myr ding electron gas, a bluish 117 30–100 Myr glimmer of synchrotron ra94 225 Myr diation is created. This is the 220 100 Myr same process as observed by 177 300 Myr physicists in large electron 70 190 Myr accelerator rings. The neutron 165 300 Myr star in M 1 is also known as >120 0.3– 0.4 Myr a pulsar from radio observa2700 150 Myr tions. 2050 100 Myr M 1 lies at a distance of 6200 light-years, which is al500 3700 Myr most five times further than ? 400 Myr to the star-forming nebulae ? 150–250 Myr M 42, M 43, and M 78, all part 229 4–6 Myr of the Orion cloud, and grea105 4–8 Myr ter still than the distances to 40 50 Myr M 8 and M 17.
process, often found to survive in the dense, dusty and opaque interior of the cloud. Here, globules are found: dense, round dark nebulae that contain a proto-star. M 42 is a good example of how the energetic ionizing radiation of the luminous hot stars forms an opening in the inner cloud of dust and gas by radiation-driven erosion, while the youngest part of the star cluster still remains hidden inside. M 20, by contrast, appears more spherical, as there is only one dominating hot star in its center, which creates an HII region equally distributed around it. Stars with cooler photospheres may be very luminous, but their weak ultraviolet radiation may not be sufficient to ionize the surrounding gas. Instead, if dust is present, their light can be reflected off the dust particles and scattered. This is what we see as a reflection nebula. Since the scattering process is more efficient in blue light, these nebulae appear bluish – like the part of M 20, which contrasts with the ionized, red H-emitting part. The only pure reflection nebula in the Messier ca-
The open clusters of the Messier catalog No.
Magnitude
Angular size
Distance
Physical size
M 45
1.5
2°
425 Ly
15 Ly
M 44
3.1
1.2º
610 ly
15 ly
M7
3.3
80'
980 ly
23 ly
M 39
4.6
30'
1010 ly
9 ly
M 42
?
3'
1300 ly
4 ly
M6
4.2
20'
1590 ly
10 ly
M 47
4.4
30'
1600 ly
14 ly
M 34
5.2
35'
1630 ly
17 ly
M 25
4.6
30'
2020 ly
17 ly
M 23
5.5
35'
2050 ly
20 ly
M 41
4.5
40'
2260 ly
26 ly
M 48
5.8
30'
2510 ly
22 ly
M 20
8.5
20'
2660 ly
15 ly
M 35
5.1
28'
2710 ly
22 ly
M 50
5.9
15'
2870 ly
13 ly
M 67
6.9
25'
2960 ly
21 ly
M 93
6.2
24'
3380 ly
23 ly
M 38
6.4
15'
3480 ly
15 ly
M 26
6.6
10'
3740 ly
10 ly
M 21
5.9
18'
3930 ly
20 ly
M 18
6.9
5'
4220 ly
6 ly
M 36
6.0
12'
4300 ly
15 ly
M8
5.8
7'
4310 ly
9 ly
M 46
6.1
20'
4480 ly
26 ly
500
500 Myr
M 37
5.6
25'
4510 ly
33 ly
2000
500 Myr
M 52
6.9
16'
4630 ly
22 ly
6000
25–165 Myr
M 29
8.0
8'
5160 ly
12 ly
69
90 Myr
M 16
6.0
21'
5600 ly
35 ly
376
2–6 Myr
M 17
?
5'
5910 ly
10 ly
2200
1 Myr
M 11
5.8
13'
6120 ly
23 ly
2900
250 Myr
M 103
7.4
6'
7150 ly
17 ly
77
178
>130
20–40 Myr 2.3 Myr
16–25 Myr
in order of their distances, based on: Kharchenko, N. V. et al.: Astrophysical parameters of Galactic open clusters, Astronomy and Astrophysics 438, 1163 (2005)
54
The open clusters Open (star) clusters, loose accumulations of a few dozen to several thousand stars, are the result of a star formation process that once consumed a dense cloud of interstellar material. Initially hidden in-
side the gaseous cloud (M 17, M 42), the hottest O-type giants emerge first (M 8, M 16). Depending on its total mass and on the gravitational interactions with its environment, a star cluster can hold together for several million to even a few thousand million years. But with time, the cluster stars are lost to the galactic disk. Large molecular clouds can create a number of neighboring star clusters of similar age that form an association. M 36 and M 37, for example, belong to the Auriga-OB-association. OB indicates that the hottest spectral types are still present in this young formation. These luminous stars burn faster and the most massive members very soon explode as supernovae. The other massive stars evolve to become red giants. M 37, M 50, and M 103 are examples of open clusters that already contain their first red giants. Hence, the youngest star clusters can be recognized by the very hot and massive stars among their members. A good example is 2-million-year-old M 8 with 9 Sgr. Even younger are the clusters still in the process of formation in M 42, M 20, and M 17. At the other extreme is M 67 with an age of 3.7 thousand million years. To a large extent, it owes its long survival to its sparsely populated galactic environment. The poorest Messier clusters are M 18 and M 39 with only 40 and 60 confirmed member stars each. They are also the smallest clusters of the Messier catalog at only about 10 light-years in diameter. The richest open cluster in the Messier catalog is probably M 52 (about 6000 stars), followed by M 11 (2900) and M 35 (2700). M 11, together with M 37, is also among the largest open clusters in general. With a diameter of 50 light-years, each is the size of a small globular cluster. Plotting the open clusters in the galactic plane around the Sun at their proper distances, we obtain a pattern that coincides with the spiral arms of our galaxy. Most of the nearer open clusters, beginning with the Pleiades at a distance of only 430 light-years, are in the Orion arm. The Sun itself lies in the inner edge of that same arm. Towards the galactic center, a number of clusters mark the Sagittarius arm. It hosts, for example, M 11, M 16, and M 8. In the opposite direction lies the Perseus arm with M 103 (at a distance of 7200 light-years) and h & F Persei. Even further away (12,000 light-years) towards the galactic edge is NGC 2158, which in the sky appears to be a close neighbor of M 35.
The planetary nebulae Messier’s catalog contains only four planetary nebulae. These objects are a by-product of the creation of white dwarfs. This is the evolutionary fate of most stars, except the most massive ones which will undergo a supernova explosion. A planetary nebula, by contrast, is formed by a gradual process: in the final, very cool supergiant stages with a highly compressed stellar core, the star’s surface gravity becomes extremely low. Under these conditions, a cool, slow, and relatively dense wind or “superwind” removes all of the remaining outer stellar layers in the final twenty- to fifty-thousand years. With the exposure of a now “naked” hot core, a much thinner, hot and very fast wind starts. As it pushes outwards, accompanied by ionizing ultraviolet radiation, an ionized shell is formed inside the cool, still slowly expanding circumstellar gas and dust – a glowing nebula with emission lines, not unlike an HII region, but for very different physical reasons. The higher densities in the shells of planetary nebulae favor [OIII] line emission over the hydrogen Balmer lines (i.e., HD, HE – the intensity ratio can
Trümpler classification of open clusters This classification scheme was introduced in 1930 by Robert J. Trümpler. Born in Switzerland, he emigrated to the USA early in the twentieth century. He thought that clusters of similar appearance (same Trümpler class) would be physically alike (e.g., have the same size). If so, the distances to open clusters could be estimated, and they could be used to trace galactic structure. The Trümpler classification has four parameters, which describe:
Appearance I II III IV
with strong central concentration, standing out well. cluster with weak central concentration, standing out well. cluster without any noticeable concentration, stars distributed thinly but evenly, standing out well. cluster, which does not stand out well from the background but appears like a concentration in the star field.
Brightness distribution of cluster stars 1 2 3
most cluster stars have nearly the same brightness. moderate brightness distribution of the stars. cluster composed of bright and faint stars, typically a few very bright and several moderately bright stars standing out from a large group of faint stars.
Number of cluster stars p m r
poor cluster with less than 50 stars. moderately rich cluster with 50 to 100 stars. rich cluster with more than 100 stars.
Additional indicators e u n
elongated. asymmetrical. contains nebulosity.
According to this scheme, M 45 has been classified as I3m, M 37 as I2r and M 39 as III2m. Today the Trümpler classification system is hardly ever used, since it is very subjective and depends on the observing method. Modern distance measurements and the determination of cluster age now rely on precise photometry of cluster stars and their colors, and a quantitative interpretation by computer models of stars and their evolution.
55
be twice as high. The ionizing power of the hot wind and ultraviolet radiation fades on a timescale of about 10,000 years. At the same time, the now aged planetary nebula begins to disperse, just like the last breath of a “dying” star. Planetary nebulae reach sizes of only a few light-years. In the Messier catalog, they span about the range of 0.7 (M 76) to 3.5 (M 97) light-years. Exact sizes and distances, however, are notoriously difficult to assess for these objects.
The globular clusters Sun
ly
ly
ly
ly
Globular clusters are dynamically stable objects, due to their large total mass. Their name relates to their mostly spherical form. About 150 of these objects are known in the Galaxy, which they surround in a widespread halo. However, that number is dwarfed by the quantity of globular clusters surrounding other galaxies, e.g., 16,000 around the giant galaxy M 87. Looking at the distribution of our globular clusters in the sky, there is a remarkable concentration towards the galactic center – the inner halo. These globular clusters are frequently found in, or crossing, our galactic disk while orbiGalactic center ting the galactic center. The nearest globular clusters have distances comparable to those of open cluThe distribution of open clusters and galactic nebulae of the Messier catalog on the galactic sters. M 4 at about 5600 light-years, for plane, within a radius of 10,000 light-years around the Sun. The nearest spiral arms are example, is nearer to us than M 11. Towards indicated. the galactic center, however, we not only see globular clusters in front of it (like M 22), but also next to it (like M 28) or on its far side (M 72). Towards M when a globular cluster has undergone a core collapse (by dynamical 75 at a distance of 78,000 light-years, our view crosses two-thirds of instability and transfer of kinetic energy out of the core region) are the galactic diameter. super-densities of up to 100,000 stars per cubic light-year reached. A A special case among the globular clusters is M 54. It is not a ga- visual measure of the degree of concentration is the classification of lactic object but belongs to the small dwarf galaxy SagDEG. Hence, at globular clusters into class I (extremely compact) to XII (very loose), a distance of 85,000 light-years, this is the most distant globular clu- analogous to the “Trümpler classes” for open clusters. While this ster of the Messier catalog. scheme has no relevance to astrophysical research any more, it is a The physical size and the mass of globular clusters differ greatly. very useful one for the visual amateur observer. The most concentrated The smallest example is M 71: with 40,000 solar masses and fewer than globular cluster in the Messier catalog is M 2 (II), the loosest examples 100,000 stars, it is not much larger than the largest open clusters. At are M 55 and M 71 (XI). Galactic globular clusters have ages of about 10 to 13 thousand the other extreme are M 19 and M 54, each with several million stars and a mass of 1.5 million solar masses, approximately that of a dwarf million years – about 100 times older than most open clusters. Having lost their interstellar matter, globular clusters cannot form new stars. galaxy. Photographs, in particular, give the impression of very high star Hence, all their member stars are very old, which is why they show densities in globular clusters. In reality, however, there are between 10 the elemental composition of earlier stages of the Universe. Elements and 1000 stars per cubic light-year at their centers – which means that heavier than hydrogen and helium can form only by the central nuclethe average distance between stars is still 0.1 to 0.5 light-years. Only ar processes of stars and supernova explosions, and they are dispersed
56
into the interstellar medium by supernovae and stellar winds to feed new star formation. Hence, globular clusters give testimony of the early Universe when heavy elements were much less abundant, and that distinguishes them from all other stellar clusters. Low abundance of heavy elements and low stellar mass bring about a special group of variables, typical for globular clusters: the pulsating RR Lyrae stars. Lacking a static equilibrium between radiation pressure and gravity, these stars oscillate over the course of a few hours and show brightness variations of about 0.5 to 2 magnitudes. In addition, there are other types of variables in globular clusters. The record holder is M 3 with 274 known variable stars, while in M 10 only four variables have been discovered so far. Luminous stars of spectral type O and B are not found in globular clusters, because these stars “die” very young. Oddly enough, a few blue stars are found in globular clusters: “blue stragglers.” Hence, these must have been formed recently – supposedly by the merging of close, old binary stars. Some globular clusters even host pulsars. The record holder in the Messier catalog is M 62 with six of them.
The galaxies
The planetary nebulae of the Messier catalog No.
Magnitude
Angular size
Distance
Physical diameter
Age
M 76
10.1
67"
2550 ly
0.7 ly
?
M 57
8.8
86" × 62"
2300 ly
0.9 ly
10,000–20,000 years
M 97
9.9
170"
4140 ly
3.5 ly
6000–12,000 years
M 27
7.4
8.4' × 6.1'
1150 ly
3.0 ly
~ 9000 years
The globular clusters of the Messier catalog No.
Magnitude
Angular size
M4
5.8
35'
M 22
5.1
33'
Distance 5640 ly 10,440 ly
Physical diameter Mass 57 ly 100 ly
Variables
100 × 103 M
65
3
78
3
500 × 10 M
M 71
8.0
7'
18,330 ly
40 ly
40 × 10 M
23
M 55
6.3
19'
19,300 ly
110 ly
250 × 103 M
40
M 12
6.8
14'
20,760 ly
85 ly
3
5
3
250 × 10 M
M 10
6.6
19'
24,750 ly
140 ly
200 × 10 M
4
M 13
5.7
21'
25,890 ly
160 ly
600 × 103 M
40, Pulsar
M5
5.7
20'
26,620 ly
150 ly
3
143
3
800 × 10 M
M 92
6.5
14'
27,140 ly
110 ly
400 × 10 M
20
M 107
7.8
13'
27,370 ly
105 ly
200 × 103 M
23
M 56
8.4
7'
27,390 ly
55 ly
3
14
3
200 × 10 M
M 30
7.3
12'
29,460 ly
100 ly
300 × 10 M
13
M3
5.9
19'
34,170 ly
190 ly
800 × 103 M
274
3
M 28
6.8
10'
34,480 ly
100 ly
500 × 10 M
19, Pulsar
M 70
7.8
8'
34,770 ly
80 ly
200 × 103 M
>10
M 62
6.7
11'
34,930 ly
110 ly
M 68
7.6
11'
36,580 ly
120 ly
M 69
7.7
10'
36,920 ly
110 ly
3
1000 × 10 M ? 300 × 103 M
>200, 6 Pulsars 42 13
An older technical term for galaxies was “extraM 15 6.0 18' 39,010 ly 200 ly 131 450 × 103 M galactic nebulae.” However, that does not reflect 3 their true nature as distant milky ways in their M2 6.4 16' 40,850 ly 190 ly 30 900 × 10 M own right, with many thousand millions of stars, 7 M 79 7.7 6' 45,000 ly 80 ly 400 × 103 M 3 thousands of open clusters, globular clusters, and M 19 6.7 14' 45,000 ly 180 ly 1500 × 10 M 8 HII regions. In the nearest galaxies, the memM9 7.6 11' 46,090 ly 150 ly 16 300 × 103 M bers of our Local Group, we are able to observe M 80 7.3 9' 48,260 ly 125 ly 10 400 × 103 M such individual objects. The Andromeda Galaxy 3 M 14 7.6 11' 55,620 ly 180 ly 1200 × 10 M 68 (M 31) in particular is a nice example of a large M 72 9.2 6' 58,510 ly 100 ly 51 200 × 103 M spiral galaxy. It has a diameter of about 160,000 3 M 53 7.7 13' 61,270 ly 230 ly 67, Pulsar 750 × 10 M light-years and 300 to 400 thousand million solar 3 46 M 75 8.6 7' 77,840 ly 160 ly 500 × 10 M masses. By contrast our other neighbor, M33, has M 54 7.2 12' 84,650 ly 300 ly 1500 × 103 M 211 only about one tenth of the mass of M 31. in order of their distances, based on: Recio-Blanco, A. et al.: Distance of 72 Galactic globular clusters, Astronomy and Astrophysics, 432, 851 (2005) With increasing distance from us, groups and clusters of galaxies become more obvious in the sky. M 81 and M 82 are 12 million light-years light-years. It is 26 times farther away than M 31, 770 times more diaway, M 51 is 27 million light-years. These form two small, widely stant than M 54, and 150,000 times farther than M 45. scattered galaxy groups with other, smaller galaxies, mostly dwarfs. Dwarf galaxies like M 32, which is tied by gravity to its mother gaA large and dense gathering of galaxies, by contrast, is the center of laxy M 31, may have diameters of only a few thousand light-years. At the Virgo galaxy cluster at a distance of 45 to 62 million light-years. the other extreme, M 101 measures about 185,000 light-years, almost About 2500 galaxies are packed within a diameter of 10 to 15 milli- twice as much as our own Milky Way. Any accurate assessment of gaon light-years, 14 of them are found in the Messier catalog. The most laxy diameters, however, is made difficult by their inclination from a distant example of all Messier galaxies is M 109 at about 67.5 million perfect face-on view.
57
Spectral types of stars and stellar evolution Very generally speaking, all stars are built the same way: in a dense, hot core, hydrogen fuses to helium. The core is surrounded by outer layers that provide the right conditions to transport the energy outside, by radiation or by convection. Depending on mass, however, stars can have very different temperatures (from 3000K to 100,000K) and densities in their photospheres. The conditions in these outermost layers can be determined by a detailed spectral analysis of the star’s light. Although developed 120 years ago, the spectral classification scheme below is still used today by professional astronomers, because it immediately gives an approximate temperature value.
11000K Rigel
7500K
6000K
4500K
5
Ib Supergiants Spica
Every spectral class is divided into 10 subclasses from 0 to 9. For very cool, red stars, there are two additional, special classes: 10000
Antares 5
4 II Bright giants
0
Mira
Capella A III Giants
Vega Sirius A
Ma
in
+5
Aldebaran A
4
IV Subgiants seq
uen
1
ce
1
Sun Dwarfs
Subdwarfs +10
Absolute magnitude
0,01
White dwarfs
Barnard´s Star O
B
A
F
G
K
M
Spectral type
The Hertzsprung-Russell diagram. The location of the main sequence and evolution tracks of two stars are plotted: A) the Sun – 1: present state; yellow main-sequence “dwarf,” hydrogen-burning in core, 2: first giant branch; hydrogenburning in shell, 3: “helium flash,” 4: helium-burning in core, 5: asymptotic giant branch; helium- and hydrogen-burning shells, mass loss by a “cool wind” leaves a white dwarf. B) massive star – 1: blue main-sequence star, hydrogenburning in core, 2: hydrogen-burning in shell, 3: smooth onset of helium-burning, 4: “blue loop;” helium-burning in core, 5: red supergiant; helium- and hydrogen-burning shells, later carbon-burning in core, mass loss by a “cool wind.”
58
Atlas of the Messier Objects Highlights of the Deep Sky The 110 star clusters, nebulae and galaxies of Messier’s catalog are among the most popular of all the deep sky objects and are beautiful targets for amateur observers of all abilities. This new atlas presents a complete account of all of the Messier objects, detailing, for each object: • • • •
its astrophysical significance well-researched background on its discovery clear observational descriptions from naked eye through to large telescopes observations and anecdotes from Messier himself and other famous observers from the past
In addition, this atlas has some of the world’s finest color astrophotos, inverted photos that have been labeled to point to hidden details and neighboring objects, and historical sketches alongside new deep sky drawings, helping to bring the Messier objects to life. Painting an engaging portrait of Charles Messier’s life and observations, this is the most far-reaching and beautiful reference on the Messier objects there has ever been, and one that no observer should be without!
RONALD STOYAN is editor-in-chief of interstellarum, one of Germany’s main astronomy magazines. He was the founding director of the German deep sky organization ‘Fachgruppe Deep-Sky’, and has authored and coauthored six books on practical astronomy. STEFAN BINNEWIES is a leading astrophotographer and travels around the world to get the best shots. He has
worked on several amateur observatory projects, including helping to establish the Capella Observatory near Windhoek, Namibia. SUSANNE FRIEDRICH is an editor for interstellarum and a visiting scientist at Max-Planck-Institute for extraterrestrial physics. A trained astrophysicist, she has been observing the sky both visually and photographically for more than 25 years. KLAUS-PETER SCHROEDER is Professor of Astronomy at the University of Guanajauto, Mexico. An avid amateur
astronomer and photographer since youth, he has published several books on astrophotography and is a regular contributor writing for amateur astronomy magazines.
Cover illustration: A majestic view of M 31, M 32, and M 110, our intergalactic neighbors. This image was taken by Robert Gendler in September and November, 2005. A 20-inch reflector was used at 4000mm focal length, total exposure was 90 hours with a SBIG CCD camera STL-11000XM, from Nighthawk Observatory, New Mexico, USA.
ATLAS of the
MESSIER OBJECTS HIGHLIGHTS OF THE DEEP SKY Ronald Stoyan Stefan Binnewies, Susanne Friedrich and Klaus-Peter Schroeder
CAMBRIDGE UNIVERSITY PRESS
Cambridge, New York, Melbourne, Madrid, Cape Town, Singapore, São Paulo Cambridge University Press The Edinburgh Building, Cambridge CB2 8RU, UK Published in the United States of America by Cambridge University Press, New York www.cambridge.org Information on this title: www.cambridge.org/9780521895545 © Cambridge University Press 2008 This publication is in copyright. Subject to statutory exception and to the provision of relevant collective licensing agreements, no reproduction of any part may take place without the written permission of Cambridge University Press. First published in print format 2008
ISBN-13 978-0-511-42329-1
eBook (EBL)
ISBN-13
hardback
978-0-521-89554-5
Cambridge University Press has no responsibility for the persistence or accuracy of urls for external or third-party internet websites referred to in this publication, and does not guarantee that any content on such websites is, or will remain, accurate or appropriate.
Dedicated to the memory of my brother Norman Stoyan (1975–2003)
Table of contents Table of contents Foreword Preface User guide
6 8 9 10
Charles Messier The Observations The Catalog Statistics of the Messier objects Visual observation of the Messier objects Photography of the Messier objects
15 25 39 53 63 68
The 110 Messier objects
71
Glossary of technical terms Index of figures Index of sources
6
357 362 365
Object
Type
Constellation
M M M M M M M M
1 2 3 4 5 6 7 8
Taurus Aquarius Canes Venatici Scorpius Serpens Scorpius Scorpius Sagittarius
M M M M M M M M M M M M M M M M M M M M M M M M M M M M M M M
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39
Galactic nebula Globular cluster Globular cluster Globular cluster Globular cluster Open cluster Open cluster Galactic nebula and Open cluster Globular cluster Globular cluster Open cluster Globular cluster Globular cluster Globular cluster Globular cluster Open cluster Galactic nebula Open cluster Globular cluster Galactic nebula Open cluster Globular cluster Open cluster Star cloud Open cluster Open cluster Planetary nebula Globular cluster Open cluster Globular cluster Galaxy Galaxy Galaxy Open cluster Open cluster Open cluster Open cluster Open cluster Open cluster
Ophiuchus Ophiuchus Scutum Ophiuchus Hercules Ophiuchus Pegasus Serpens Sagittarius Sagittarius Ophiuchus Sagittarius Sagittarius Sagittarius Sagittarius Sagittarius Sagittarius Scutum Vulpecula Sagittarius Cygnus Capricornus Andromeda Andromeda Triangulum Perseus Gemini Auriga Auriga Auriga Cygnus
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Object
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Object
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M M M M M M M M M M M M M M M M M M M M M M M M M M M M M M M M M M M M M M M M
Optical double star Open cluster Galactic nebula Galactic nebula Open cluster Open cluster Open cluster Open cluster Open cluster Galaxy Open cluster Galaxy Open cluster Globular cluster Globular cluster Globular cluster Globular cluster Planetary nebula Galaxy Galaxy Galaxy Galaxy Globular cluster Galaxy Galaxy Galaxy Galaxy Open cluster Globular cluster Globular cluster Globular cluster Globular cluster Globular cluster Asterism Galaxy Globular cluster Planetary nebula Galaxy Galactic nebula Globular cluster
Ursa Major Canis Major Orion Orion Cancer Taurus Puppis Puppis Hydra Virgo Monoceros Canes Venatici Cassiopeia Coma Sagittarius Sagittarius Lyra Lyra Virgo Virgo Virgo Virgo Ophiuchus Canes Venatici Coma Leo Leo Cancer Hydra Sagittarius Sagittarius Sagitta Aquarius Aquarius Pisces Sagittarius Perseus Cetus Orion Lepus
170 171 173 183 184 187 193 195 197 199 201 203 208 210 212 213 215 217 224 226 228 230 233 235 238 241 245 248 250 252 253 254 256 258 259 262 264 266 269 272
M M M M M M M M M M M M M M M M M M M M M M M M M M M M M M M
Globular cluster Galaxy Galaxy Galaxy Galaxy Galaxy Galaxy Galaxy Galaxy Galaxy Galaxy Galaxy Globular cluster Open cluster Galaxy Galaxy Galaxy Planetary nebula Galaxy Galaxy Galaxy Galaxy Galaxy Open cluster Galaxy Galaxy Galaxy Globular cluster Galaxy Galaxy Galaxy
Scorpius Ursa Major Ursa Major Hydra Virgo Coma Virgo Virgo Coma Virgo Virgo Coma Hercules Puppis Canes Venatici Leo Leo Ursa Major Coma Coma Coma Ursa Major Draco Cassiopeia Virgo Leo Canes Venatici Ophiuchus Ursa Major Ursa Major Andromeda
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40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79
80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110
7
Foreword David H. Levy Why yet another Messier catalog book? With Kenneth Glyn-Jones,
What if Messier were to return to our time? He would be amazed
Stephen James O’Meara, and Ken Graun, haven’t we had enough?
at the ease by which visual comet hunting can be done, as well as the
No, I say! And especially no when the latest addition to the canon is
increased difficulty in finding a comet when well-funded electronic
Ronald Stoyan’s scholarly, historical, astrophysical, and superb look at
searches compete with amateur astronomers. With a computer star
the great comet hunter and the list of objects he compiled during his
chart riding with my telescope, I know instantly what my telescope is
lifetime.
showing at any particular moment. On the morning of October 2, 2006,
This book is the first scholarly look at the catalog since Glyn-Jones,
for example, the chart showed a rich field of stars with the planet Sa-
and that effort is almost half a century old. Stoyan explores the latest
turn in the field center; it did not display, however, the faint fuzzy spot
astrophysical research concerning each of Messier’s 110 deep sky ob-
that turned out to be my 22nd comet discovery, a new comet that will
jects. Stoyan could well devote his entire book to the astrophysics of
make a close approach to the Earth when it returns at the end of 2011.
Messier’s first object, the Crab Nebula, and I still subscribe to the belief
Messier obviously did not have such technology at his disposal; he used
that I read years ago that astronomy has two parts: that of the Crab and
his telescope and a printed star atlas, trusted friends that remained the
that of everything else. From the first time I looked at M 1 on September
classic way to search the sky until just a few years ago.
1, 1963, I’ve been fascinated by the ghostly luminescence of the Crab,
For all of Messier’s brilliance, his famous catalog was primarily an
but never more so than when it seemed ablaze again not with a new
observing tool, and Stoyan’s writing confirms this crucial footnote to
supernova, but with nearby Saturn visiting at nearly the same spot from
history: by keeping a record of the objects that could be mistaken for
which the original star first became visible on July 4, 1054.
comets, Messier provides himself and posterity an invaluable resource.
Next comes the historical view: I cannot get enough of the life
The pages you are about to read delve further into what his list looks
of Charles Messier, who lived, observed, searched, and suffered some
like after 200 years, and particularly the astrophysics that lies behind
two hundred years ago. This observer’s life story is compelling, and
each of the clusters, nebulae, and remote galaxies that constitute it.
Stoyan’s retelling adds new material. Although he was not the first
Stoyan does not take a position on one of the questions of our time –
person to discover a comet with a telescope, Messier was most likely
should the double cluster in Perseus be added to the list?
the first to organize a successful survey program specifically devoted
Yes, there is a need for “yet another” Messier catalog book. Stoyan
to the search for comets. For that accomplishment he certainly deser-
has done a masterful job giving his readers a modern look at Messier’s
ves a place with the greats like William Herschel, Kaoru Ikeya, and
greatest accomplishment. May this book inspire you to learn about the
Leslie Peltier. In Stoyan’s biographical summary we learn a little more
man and his project, and more importantly, may it encourage you to
about Messier’s famous accident, in which he fell into a pit. Although
don a coat, grab a telescope, and enjoy this window into the deep sky
he recovered enough to resume his work, we know for the first time
for yourself.
that he never completely got well again, and he finished his life with a continuing limp. A fortunate fall, to be sure, for he is lucky to have survived it in the first place.
8
Preface
The catalog gathered by the French astronomer Charles Messier (1730–1817) has been the most popular compilation of astronomical objects beyond our Solar System for more than 200 years. It contains 110 star clusters, nebulae, and galaxies, among them most of the brightest and finest deep sky highlights that are visible from northern skies. Amateur and professional astronomers alike have turned their telescopes time and again to the Messier objects. Numerous books have covered them, and numerous websites attest to their unwavering popularity. However, a current overall picture of the catalog and its objects was missing, as much information currently disseminated is actually outdated. So, for the first time since Robert Burnham’s famous Celestial Handbook, a thoroughly investigated new account with historical, astrophysical, and observational information on all the objects had to be conducted. Many discrete tasks were associated with this book. Historical information on Charles Messier, his observations and his catalog had to be compared to latest level of knowledge. In addition to our own research, the biography published by Jean-Paul Philbert in the French language proved especially helpful. The main task was the compilation of recent astrophysical information on all of the objects. More than 500 scientific papers were compiled and evaluated. These texts are complemented by extensive observational notes, which incorporate the visual use of large modern reflectors. A major part of the book is the more than 150 fantastic photos by leading amateur astrophotographers from all over the world. Occasionally, these images are accompanied by photographs from the Hubble Space Telescope, where this adds value. In addition, an extensive collection of visual drawings is shown, both from the classical era of the nineteenth century, as well as modern sketches drawn by the author himself. The compilation of this book took much effort over the past five years. Many of the images were prepared exclusively from such exotic
spots as Greece, Chile, and Namibia. They combine more than 5000 minutes of photographical exposure and 150 hours of visual observation. From the original German edition, which was released in 2006, information and photos have been updated and improved. I owe a very personal thank you to the co-authors of this book. Stefan Binnewies, the well-known German astrophotographer, conducted the orchestra of his colleagues. Susanne Friedrich, professional astronomer and amateur alike, ensured the quality of the astrophysical information. Finally, Prof. Klaus-Peter Schroeder, also a professional astronomer, who has worked in the United Kingdom and the United States for decades, translated and updated the texts. A deeply felt thank you goes to the astrophotographers who contributed so much to this book, especially to the teams of Volker Wendel and Bernd Flach-Wilken, Josef Pöpsel and Dietmar Böcker, and Robert Gendler and Jim Misti. I would also like to thank Lutz Clausnitzer, Klaus Wenzel, Arndt Latusseck, Wolfgang Steinicke and Matthias Juchert, who helped in many respects on the German edition. The fact that this book appears in an English language edition is almost a miracle. Among the many people who have helped that this dream became reality are Owen Brazell, David Eicher, Phil Harrington, Yann Pothier, and Stewart Moore. Additionally, I am greatly indebted to Sue French, who proofread the manuscripts and supported this project to a very great extent, and David Levy, who authored the foreword in his unparalleled manner. Finally, I would like to thank Vince Higgs and the team at Cambridge University Press for their support, work, and faith. May this book give you new insights into your favorite deep sky highlights.
Erlangen, Germany Ronald Stoyan
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User guide The data files Degree of difficulty: rating of the observational difficulty: 1 object easily visible to the naked eye 2 object difficult to see with the naked eye 3 object easily visible in 8×30 binoculars 4 object easily visible in 10×50 binoculars 5 object difficult to see with 10×50 binoculars For more information about visual and photographic difficulty, see page 63. Minimum Aperture: minimum aperture required to see the object under a dark mountain sky, according to the personal experience of the first author. There are four categories: • naked eye • 15mm • 30mm • 50mm Designation: catalog number in the NGC (New General Catalogue) or the IC (Index Catalogue). Type: Object type. For a more detailed introduction to the different types, see page 53. Class: Classification of the object, specific to its type: • Galactic nebulae: distinction between emission nebula and reflection nebula, see page 53 • Open clusters: Trümpler classification, see page 55 • Globular clusters: concentration class, see page 56 • Galaxies: Hubble classification scheme, see page 61
• galaxies: H2000 (multiple authors: “The Hubble Space Telescope Key Project on the Extragalactic Distance Scale,” Astrophysical Journal 529, 698, 745, 786 (2000) • Virgo cluster galaxies: V2004 (Sanchis, T., et al.: “The origin of HI-deficiency in galaxies on the outskirts of the Virgo cluster. II. Companions and uncertainties in distances and deficiencies,” Astronomy and Astrophysics 418, 393 (2004) • Virgo cluster galaxies: V2002 (Solanes, J.M., et al.: “The Threedimensional Structure of the Virgo Cluster Region from TullyFisher and HI data,” Astronomical Journal 124, 2440 (2002) • extragalactic HII regions: HK83 (Hodge, P.W., Kennicutt, R.C., Jr.: “An atlas of HII regions in 125 galaxies,” Astronomical Journal 88, pp. 296 (1983) In addition, alternative results have been quoted, in order to demonstrate the uncertainty of the distances given. If available, the distance measurement method is indicated. Size: physical diameter of the object, as calculated from its actual distance and angular diameter. The resulting values may differ from the ones stated by original sources. Spiral galaxies seen under some inclination may be underestimated. Constellation: Latin name of the constellation in which the object is located R.A.: Ascension for the equinox 2000.0 Decl.: Declination for the equinox 2000.0 Magnitude: apparent total visual brightness
Distance: Distance from Earth in light-years. As far as possible, uniform sources have been used, i.e.: • galactic nebulae and open clusters: K2005 (Kharchenko, N.V., et al.: “Astrophysical parameters of galactic open clusters,” Astronomy and Astrophysics 438, 1163 (2005) • globular clusters: Rww2005 (Recio-Blanco, A., et al.: “Distance of 72 galactic globular clusters,” Astronomy and Astrophysics 432, 851 (2005)
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Surface brightness: mean visual brightness in magnitudes per square arcsecond (not given for star clusters) Apparent diameter: apparent (angular) photographic diameter
The texts History
Observation
The historical sections include translations from the original quotations of historic observers from the seventeenth to the early twentieth century. In part, these have been translated from the original. Where not available, they had to be taken as quotes from secondary literature. English quotations are given, as far as available, in their original wording. Frequently, the term “resolution” (of an object) is used in historic texts – not just for star clusters, but for galaxies and nebulae as well. In the nineteenth century, that did not necessarily mean the resolution into individual stars, as we use the term today, but rather resolution of any kind of detail. A short introduction to every historic observer quoted in this book can be found on page 28.
The information and advice given for the visual observation of each object is based on the personal experience and observation of the first author, using telescopes of different apertures. Each object has been observed on several occasions, some more than a dozen times. The instrumentation used consisted of: • 3.5×15 opera glass, “Theatis” made by Carl Zeiss Jena • 8×30 binoculars, “Deltrintem” made by Zeiss Jena • 10×50 binoculars, “Dekarem” made by Carl Zeiss Jena • 20×100 binoculars, made by Miyauchi • 120/1020mm (4.7-inch) refractor “Star 12ED,” made by Astro-Physics, magnifications from 25× to 255×, in exceptional cases 340× and more • 360/1780mm (14-inch) Newtonian on a Dobsonian mount, magnifications from 45× to 593×, entirely manual operation, observing sites in the German countryside (Kreben, naked-eye limiting magnitude 6.5, sky surface brightness 21.0 mag/arcsecond2) and Austrian Alps (Tiefenbachferner, naked-eye limiting magnitude 7.0 mag, sky surface brightness 21.6 mag/arcsecond2) • 500/2500mm (20-inch) Newtonian on a Dobsonian mount, magnifications from 63× to 625×, Farm Tivoli, Namibia (naked-eye limiting magnitude 7.5, sky surface brightness 21.8 mag/arcsecond2)
Astrophysics Ever since the publication of the famous “Burnham’s Celestial Handbook” in the 1970s, amateur astronomers have been waiting for a new, up-to-date compilation of astrophysical data on all Messier objects. A lot of literature, internet sources in particular, refers to outdated values. For this book, the content of over 500 professional, up-to-date publications was researched. This was made possible by the use of the Internet and the free NASA service known as the Astrophysical Data System (ADS), which is an on-line collection of almost all scientific publications in astronomy. The exact citations are given in the Appendix. Where possible, no sources older than 10 years were used, but a few objects have received little attention in modern references. Other objects (M 1, M 31, M 42) catch a lot of professional attention, and the vast amount of literature dealing with them would easily permit a much more detailed treatment. However, space restrictions limited this book to the most relevant information. In many cases, the research presents surprises: modern scientific results often disagree completely with what is commonly believed as the result of outdated literature. This trend will continue, as there is a steady stream of new observations and their astrophysical interpretation. Hence, the statements made in this book must be regarded as only a momentary picture of our knowledge from the years before 2007. Many questions remain unanswered, and we expect new insight into topics such as dark matter, black holes or the age of the Universe. This may affect how some aspects of the Messier objects will be explained in the future. Another common problem is the disagreement of modern sources from one another. Different authors have different opinions, and different methods yield different results. Generally accepted knowledge grows out of long debate and testing. This is part of the lively nature of a quickly developing science such as modern astrophysics.
Observing comments refer to a very experienced observer and excellent observing sites with a dark, moonless sky. We have purposely omitted star charts and all advice on finding the objects, since there is already a vast literature on these aspects, useful even to the first-time observer. However, we recommend a versatile software-based approach, “Eye & Telescope.” It produces star charts and visibility information based on actual sky conditions and the instrument used.
11
The pictures Selected images showcase the fantastic results of the amateur astrophotographer’s community. To document astrophysical aspects beyond the reach of amateur photos, we have complemented the material with NASA pictures of many Messier objects, obtained by the Hubble Space Telescope (HST). Some Messier objects are particularly popular with amateurs, and good images are abundant. Others grab almost no attention and only a few pictures of lower quality are available. It’s virtually impossible to get photos of uniform quality for all 110 objects. For this reason, the scale and depth (i.e., limiting magnitude) of the photos vary from object to object. The photos printed in this book were taken in the years between 1995 and 2007. The most common technique is tri-color (red, green, blue) photography with a cooled CCD camera and (L)RGB filter wheel. With a few exceptions, traditional film-based photography can no longer compete, while the new era of digital cameras and DSLRs is just about to begin. For accurate technical information on each picture, refer to the picture credits in the appendix section. The color reproduction is neither uniform, nor should it be regarded as quantitatively correct. Color-balance and saturation depend on a number of factors, such as chip-characteristics, filter-transmission, software and personal judgment during image processing. The result is often subjective, perhaps aimed at reproducing the colors of professio-
nal photos. After all, techniques of absolute color calibration are timeconsuming and do not apply to some types of astronomical objects, most notably the emission nebulae. The techniques used by amateur astronomers for their image-processing work differ a lot from person to person, and there are no general standards. Some photographers would remove traces of planetoids, satellites or ghost-images by hand, on a pixel-to-pixel basis, others accept them as part of the authentic picture. Composite images made from several different exposures change the perception of the intensity range. This technique is used to accommodate large intensity variations and to avoid “burnt-out” central regions. But it may make stars on bright nebulous background appear significantly less brilliant than they are in reality. A good example is the Trapezium in the Orion Nebula. Hence, a quantitative interpretation of such a photo is impossible, but amateur astrophotographers are happy to accept that, in order to produce the most appealing image of an object. Together with the photographs, historical and modern drawings have been reproduced here. The manual sketch of an object as perceived through the telescope eyepiece was the only scientific method of recording until the late nineteenth century, after which photography finally took over. This book shows a large number of fine sketches from the pre-photographic era. Differentiating real physical changes in the objects from artistically diverse sketching styles and personal
A photo in the works: M 42. At left is a single image taken with the green filter, in the middle a raw tri-color image, at right the fully processed LRGB composite.
12
perceptions had been a continual problem. Today, amateurs keep the tradition of astronomical drawings alive, in order to sketch their visual impression of a specific object. Drawings are subjective and contain erroneous perceptions. Nevertheless, this method is an independent recording technique, complementary to the capabilities of photography. Before criticizing historical drawings for their misconceptions, we should keep in mind that it is always easier to verify a known feature than to discover it. In that sense, the historic drawings must be regarded as more “honest” than their modern counterparts. Even the most critical modern observer cannot avoid the subconscious knowledge of an object by modern photography and its influence on his or her perception of it. Drawings differ from photographs in a number of ways. For one, the eye can not accumulate light over a long time, as a photographic emulsion or chip can. Furthermore, the visual response to a large brightness range is much more logarithmic than the photographic response. And finally, the spectral response of the eye also differs from that of photographic emulsions or chips. With emission nebulae, in particular, visual and photographic views emphasize different features. The author’s drawings were specifically made for this book. The objects were observed several times with different apertures. Frequently, several attempts were required before an acceptable result was achieved. All the sketches are of a cumulative nature: each drawing summarizes the visual impressions of an object collected over many hours or even nights under a dark sky in the countryside, in the mountains or in the Namibian desert. The results are not to be confused with a quick sketch made by the eyepiece! The observing time involved was at least an hour, as for a simple elliptical galaxy, and up to three nights for large objects with a lot of detail. The original sketches are drawn with pencil, black on white. So are the proper drawings, using in addition an eraser and a smudging tool. For an inversion to white on black, the drawing is scanned and the tonal range adjusted, but no further digital manipulations are made. Subtle contrasts are over-pronounced by the drawings, as they would otherwise be lost in print.
A drawing in its work-stages: M 42. Above is the original pencil sketch, below the properly redrawn and then inverted result.
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14
Charles Messier
1730 to 1751: Childhood and adolescence Charles Messier was born on the 26th of June 1730 in Badonviller, as the tenth child of the court bailiff Nicolas Messier (1682–1741) and his wife Françoise (maiden name Grandblaise, deceased 1765). His home village lies near the former German–French language border in the western part of the Vosges Mountains in Lorraine. In Messier’s days, that region did not belong to France but to the independent dukedom of Salm. The Messier family was one of the richest in the little state, with high-ranking positions and excellent connections, which would later be very helpful to the young Charles. He grew up in a house opposite the evangelic church of Badonviller, by a square which today bears his name. Six of his siblings died in their early childhood. An important role in Charles’ life was played by his eldest brother Hyacinthe, who was older by 13 years. Hyacinthe started his professional career as an auctioneer and, eventually, became the highest financial officer of the dukedom. When their father died in 1741 – Charles was only 11 years old then – Hyacinthe was already able to take care of the Messier family. He gave Charles an apprenticeship in his office, mostly involving paper work. That helped develop the boy’s good writing and drawing skills, and the accuracy required for finance and business. His first interest in astronomy was sparked by the large, six-tailed comet of 1744, discovered by the Swiss de Chéseaux, and the annular solar eclipse of 1748. The year 1751 brought important changes to the life of the Messiers. The dukedom of Salm lost its independence by becoming part of Lorraine, which later fell to France by annexation. Only the former residence of the dukes of Salm, the village Senones, a few kilometers from Badonviller, retained its independence and was to become the new home of the Messier family. Now at the age of 21, it was time for Charles to seek a life of his own. With the help of a good family friend, who had contacts in important circles in Paris, an assistantship at the new Naval Observatory in Paris became available to Charles Messier. It was not really his interest in astronomy which got him the offer, but his good skills as an office assistant. He left Badonviller on the 23rd of September 1751.
Charles Messier at the age of 40, painted by Ansiaume. Messier commented that his portrait was most appropriate but made him look younger than he really was.
15
1751 to 1757: Assistant of the Naval Observatory
Drawing of the Hôtel de Cluny, from the beginning of the nineteenth century. The octagonal sheltered platform of the tower is Messier’s observatory.
Today, the Hôtel de Cluny is one of the most beautiful medieval buildings of central Paris. It hosts the National Medieval Museum, but there is no commemoration of the work of Charles Messier.
16
Joseph-Nicolas Delisle (1688–1768), who taught mathematics and astronomy at the Collège Royal in Paris (later to be the Collège de France), built a private observatory on the stairtower of the Hôtel de Cluny in 1747, opposite to the Collège Royal. Originally, the Hôtel de Cluny was the Parisian residence of the Benedictine monks from the great abbey in Burgundy. Later, it became the property of the French Navy. In 1754, the aged Delisle made a deal: he signed over the observatory to the Navy and in return, he received the custom-tailored title “Astronomer of the Navy.” Delisle’s humble observatory stood in the shadow of the established Royal Observatory of Paris, which was well known as a leading European institution for astronomers like Huygens, Cassini, and Maraldi. Delisle, by contrast, was not part of the French astronomy establishment. Hence, Messier entered a professional environment which allowed him to pursue his astronomical interests without any scientific obligations, but which also branded him from the outset as an outsider to professional astronomy. The childless Delisle couple received and hosted Messier as though he were their own son, and he lived with them in their apartment in the Collège. Delisle’s assistant Libour introduced Messier to the basics of astronomy, and the young Messier’s first tasks were to make hand-drawn copies of maps and to write the observing logs. Delisle had been in personal contact with the late, famous English scientists Newton and Halley. The latter had pointed out in his famous work of 1705 that the comet apparitions of 1456, 1531, 1607, and 1682 were due to the same physical comet, which would reappear in 1758. Delisle made an independent calculation of the comet’s orbit and derived April 1759 for the perihelion passage. Based on his master’s work, Messier drew a map of the comet’s path among the stars and had orders to watch for it from the summer of 1758 onward. That comet hunt was the first real astronomical task given to the 28-yearold, who so far had carried out only basic observations. Messier understood that this was the chance of a lifetime; he wanted to be the first to prove Halley’s milestone work. But life took a different course. While Messier did rediscover the comet on the 21st of January 1759, he soon had to learn that a farmer in Saxony had beaten him by about a month: the previously unknown amateur astronomer Johann Georg Palitzsch (1723–1788) from Prohlis near Dresden had already spotted Halley’s Comet on Christmas night 1758. Messier had confined his search to Delisle’s orbital path for too long. And to his great dismay, Messier could not even get his master’s permission to publish his independent discovery, since Delisle did not believe that he’d made a mistake in his calculations. He thought the comet was an unrelated object. Messier bowed to the wishes of his master and host and withheld his obser-
1
2 City map of Paris from the year 1771. The Hôtel de Cluny (1) and the Royal Observatory of Paris (2) are circled.
17
Custos Messium – a constellation for the comet hunter In 1775, the first version of the now enormously popular Messier catalog of 110 nebulae had been out for one year, with then only 45 objects. However it was his achievements as a recordbreaking comet discoverer that made Charles Messier the publicly bestknown astronomer of his country. In fact, Messier had discovered practically all the comets of the past 15 years. He had been a member of the elite circle of the French Academy of Sciences since 1770. But now, a very special honor was awarded to him, unprecedented in the history of astronomy. Jerôme de Lalande (1732-1807), a famous author, professor and colleague of Messier, created a new constellation on his freshly published stellar globe: “Custos Messium” (lat.), the “Harvest Guardian.” Concerning his motives, Lalande wrote: “This name will remind future astronomers of the courage and diligence of our industrious observer Messier, who since 1757 appears occupied with the sole task of patrolling the sky to discover comets.” Contemporary French star charts happily included the new constellation under its French name “Messier,” picturing a guardian who watched over a cornfield. The “Harvest Guardian” had its place north of Cepheus, Cassiopeia, and Camelopardalis. Today, its space has become part of these three constellations. Messier’s constellation held only one noticeable star, 40 Cas, and no remarkable deep-sky objects. As Messier related, Lalande chose that particular part of the sky, because it once hosted the comet of 1774, discovered by Montaigne. It was the only one of 14 comets that, following the death of his wife, Messier failed to discover himself. These were two big losses, which Messier could not bear – and Lalande must have been aware of that. Lalande created two other new constellations: “Felis,” the cat (between Hydra and Antlia), in memory of his favorite pet, and “Globus Aerostaticus” (between Capricornus
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The constellation Custos Messium (Harvest Guardian), pictured in Johann Elert Bode’s “Vorstellung der Gestirne” (1782).
and Piscis Austrinus) to commemorate the invention of the hot-air balloon by the brothers Montgolfier and their first air-borne voyage in 1799. All three constellations were included in J.E. Bode’s Prussian star atlases – despite, certainly, some national rivalry. But in return, Lalande would include in his atlases the “Brandenburg Scepter,” “Frederick’s Honor,” and the “Mural Quadrant,” which Bode had invented. Nevertheless, all these new constellations fell out of use only 80 years later.
Joseph Jérôme le Français de Lalande, colleague and friend of Messier. Engraving by André Pujos.
vations for three months, until it was finally clear that Delisle was wrong. However, the long-delayed publication aroused suspicion and skepticism among the royal astronomers in Paris. His independent discovery was not acknowledged – a disappointment that Messier would not forget for a long time. In hindsight, we know that the by-products of Messier’s diligent comet hunt were much more rewarding. In August 1758, when he was observing the comet discovered by de la Nux, Messier came across a yet unknown nebula which looked exactly like the comet. This discovery sparked the idea for his catalog, which retains Messier’s name to this day. Hence, Messier made good use of that chance of a lifetime, after all – albeit in quite a different way than he, the comet enthusiast, had anticipated.
Johann Georg Palitzsch succeeded in what Messier tried in vain: he was the first to rediscover Halley’s comet on its return in 1758.
1759 to 1770: Comet discoveries and recognition Comet hunting became an obsession for Charles Messier. Between 1758 and 1804, he spent more than 1100 nights on this task. He became the first real “comet hunter" in history, with a prototypical character: a most diligent observer with humble equipment but much enthusiasm, who would search for new comets with systematic endurance. He observed 44 comets altogether, more than were known to science before him. He discovered 21 comets, 6 of which are regarded today as codiscoveries. Messier was, in fact, the first observer who systematically used the telescope for comet hunting. Before him, comets were usually discovered with the naked eye. But he did not leave it with the discovery of a comet. He would observe every comet for as much and as long as possible; his record was 71 nights over a period of 6 months. Furthermore, Messier measured comet positions to make orbit calculations possible. He never did that himself, though, as he was entirely devoted to observation. None of his many publications would contain a single bit of math or theoretical work. In that respect, Messier’s close friendship with Jean Baptiste Gaspard Borchart de Saron (1730–1794) was most beneficial. Saron came
Joseph Nicolas Delisle, teacher and benefactor of Messier. Engraving by Konrad Westermayr.
from an established, noble family and was soon to become the royal state-attorney, and later even president of the parliament. Theoretical astronomy was one of his hobbies – a perfect match: Saron’s quick calculations were essential to Messier’s success, because these allowed him to find a comet again, even after a long period of bad weather. For the discovery of the great comet of 1760, Messier was still a day late. But only a few days later, on the 26th of January 1760, he discovered the first comet named after him. In the following years, Messier nearly achieved a monopoly on comet discoveries: all eight known comets between 1763 and 1771 were discovered by him! Messier was active in other respects, too. Between 1752 and 1770, he observed 93 lunar occultations and 400 eclipses of Jupiter’s satellites, he watched 5 solar eclipses, 9 lunar eclipses, and he measured 400 stellar positions. Over the course of his lifetime, Messier followed four Mercury and two Venus transits, and he did a lot of planetary observing, especially on Saturn. In 1767, he made a three-month-long sea cruise to test astronomical clocks on the coasts of the Netherlands and Belgium. Recognition by the international science community was soon to follow. In 1764, he became elected a fellow of the English and Dutch scientific academies. Such academies were of crucial importance in the eighteenth century. Only their membership made it possible to exchange correspondence with the leading scientists of the time and gave access to the accumulated knowledge of their libraries. Messier had to wait a long time for admission to the French academy of the sciences – in Paris, the skepticism aroused by his long withheld observations of Halley’s comet were still not forgotten. But, at least, his salary was raised in 1765, after the retirement of Delisle from active research. Messier’s breakthrough with the French astronomy establishment came with his discovery of the great comet of the year 1769. That comet was a spectacular sight, and it made its discoverer’s name so popular with the general public that the king would personally receive a map drawn for him by Messier. The king nicknamed Messier “the comet nest-robber,” because for many years not a single comet “slipped out of its egg” that hadn’t already been discovered by Messier. This idea then developed into the popular nickname “the comet-ferret.”
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The role-model: Nicolas-Louis de Lacaille Nicolas-Louis de Lacaille (1713–1762) was born on the 15th of May 1713 in Rumingy near Reims. As a son of noble parents, he began to study theology in Paris. He was 26 when he made his first recorded astronomical observations. Soon, he became professor at the Collège Mazarin in Paris, where in 1746 he constructed an observatory, and finally in 1741 he was admitted to the French Academy of Sciences, with the support of the Duke of Bourbon. Lacaille was well known for his accurate observations and an overeagerness to work – in fact, he died of overwork on March 21st, 1762. Hence, in 1751, the French academy chose him for a longer stay at the Cape of Good Hope, in order to accurately measure geographic longitudes and the positions of southern stars. Meanwhile, his scholar Lalande was his counterpart in Berlin for a program of simultaneous observations, which led to improved distance measurements of the planets and the Moon. Lacaille arrived in South Africa in April 1751. At the foot of Table Mountain, which he honored with the constellation “Mensa,” he began the observations for a southern star catalog in August 1751. For that work, Lacaille used a mural quadrant, equipped with a very small telescope of only ½-inch (12.5mm) aperture Abbé Nicolas-Louis de Lacaille, and a magnification of 8×. painted by Melle Le Jeuneux, A year later, in July 1752, 1762 this catalog contained the positions of 9776 stars. While cataloging the heavens, Lacaille made a list of the nebulous objects he came across, which he published in 1755. It was the first of its kind, and it is appended to Messier’s third and final catalog. Thirteen new southern constellations were created by Lacaille as a by-product of his work: Antlia, Caelum, Circinus, Fornax, Horologium, Mensa, Microscopium, Norma, Octans, Pictor, Reticulum, Sculptor, and Telescopium. With these, Lacaille filled in the coarser pattern of southern constellations created 150 years earlier by Keyzer. In addition, Lacaille changed the name of the constellation Abies into Musca – not to be confused with a lost northern constellation of that name – and he suggested splitting the huge constellation Argo Navis into Carina, Vela, Pyxis, and Puppis. About 100 years later, these suggestions became widely accepted as astronomical conventions.
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The next year (1770), Messier discovered a comet, which was identified by the Swedish observer Lexell as a periodic comet. Two weeks after that discovery, Messier was finally admitted to the French Academy of Sciences, followed by membership in nearly all of the remaining foreign scientific associations. In addition, he received another pay rise and, in 1771, he inherited the title invented for Delisle, “Astronomer of the Navy.”
1770 to 1789: Changing private fortunes and observational successes On the 26th of November 1779, Messier married the daughter of a noble professor, Marie-Madeleine Dordolot de Vermauchampt, who was three years his junior. For 15 years, they had lived under the same roof in the Collége Royal. But in the absolutistic France of that time, a marriage between a bourgeois and a noble lady would have been impossible. Only the recent great success of Charles Messier changed their fortunes. In 1771, they moved into an apartment of their own in the Hôtel de Cluny – it was then only a few steps from Charles’ bedroom to the observatory. 1771 must have been one of the best years in Messier’s life. Besides his personal good fortune, he discovered two comets and completed the first version of his catalog, then totalling 45 nebulous objects, although Messier considered the latter a mere by-product of his searches, as he just wanted to avoid confusion when he was comet-hunting. On the 15th of March 1772, there was another reason for Messier to rejoice: his wife gave birth to a son, Antoine-Charles. But then his fortunes changed dramatically: a week later, Marie-Madeleine Messier died of puerperal fever, and the little baby followed her on the 26th of March. Messier’s reaction to this heavy double-blow to his private life is difficult to assess. The fact is, however, that he started a four-day observing campaign on comet Montaigne – the first comet in almost 10 years which had not been discovered by him – the very night his son died. In August 1772, Messier travelled to the dukedom of Salm, which in his own words he regarded as his “Fatherland.” He stayed some time with his eldest brother in Senones, following earlier visits in the years 1758, 1762, and 1770. Not surprisingly, Messier continued an intense observing schedule during that family visit. On his return to Paris, he was accompanied by his nephew Joseph-Hyacinthe and by his sister Barbe, who would take care of her brother until her death in 1797. The following years were characterized by continued comet observations. In 1780, Messier published the second version of his catalog, which contained 68 nebulous objects. The first new objects were found soon after his original catalog was printed. But Messier did not keep looking systematically for new objects, he just recorded accidental findings during his comet observations. Nevertheless, the third version of his catalog, with 103 objects, came out in 1781. This was mostly due to the wealth of input from his new colleague Pierre Méchain (1744–1804). Despite more such discoveries by Méchain after 1781, there were no further catalog versions.
Table: 44 comets, observed by Charles Messier Popular name
Old designation
Messier’s first observation
Messier’s last observation
Number of nights observed
Date of discovery
Discoverer
Aug 14,1758
Nov 2,1758
31
May 26, 1758
de la Nux
P/Halley
1759I
Jan 21, 1759
May 1, 1759
47
Dec 25, 1758
Palitzsch
Great Comet
1759III
Jan 8, 1760
Jan 30, 1760
6
Jan 7, 1760
Chevalier
Messier
1759II
Jan 26, 1760
Mar 18, 1760
22
Jan 26, 1760
Messier
May 28, 1762
Jul 5, 1762
20
May 17, 1762
Klinkenberg
Messier
1763
Sep 28, 1763
Nov 24, 1763
29
Sep 28, 1763
Messier
Messier
1764
Jan 3, 1764
Feb 11, 1764
16
Jan 3, 1764
Messier
Messier
1766I
Mar 8, 1766
Mar 15, 1766
8
Mar 8, 1766
Messier
P/Helfenzrieder
1766II
Apr 8, 1766
Apr 12, 1766
5
Apr 8, 1766
Helfenzrieder
Messier
1769
Aug 8, 1769
Dec 1, 1769
42
Aug 8, 1769
Messier
P/Lexell
1770I
Jun 14, 1770
Oct 3, 1760
47
Jun 14, 1770
Messier
Great Comet
1770II
Jan 10, 1771
Jan 20, 1771
4
Jan 10, 1771
Messier
Messier
1771
Apr 1, 1771
Jun 15, 1771
48
Apr 1, 1771
Messier
Mar 26, 1772
Apr 3, 1772
4
Apr 8, 1772
Montaigne
Messier
1773
Oct 12, 1773
Apr 14, 1774
71
Oct 12, 1773
Messier
Aug 18, 1774
Oct 25, 1774
41
Aug 11, 1774
Montaigne
63
Jan 6, 1779
Bode
Bode
1779
Jan 19, 1779
May 19, 1779
Messier
1780I
Oct 27, 1780
Nov 28, 1780
13
Oct 27, 1780
Messier
Méchain
1781I
Jun 30, 1781
Jul 16, 1781
14
Jun 28, 1781
Méchain
Méchain
1781II
Oct10, 1781
Nov 5, 1781
12
Oct 9, 1781
Méchain
Nov 27, 1783
Dec 21, 1783
13
Nov 19, 1783
Pigott
Feb 3, 1784
May 25, 1784
13
Jan 24, 1784
Cassini
Messier
1785I
Jan 7, 1785
Jan 16, 1785
6
Jan 7, 1785
Messier
Méchain
1785II
Mar 13, 1785
Apr 16, 1785
14
Mar 11, 1785
Méchain
P/Encke
1786I
1
Jan 17, 1786
Aug 1, 1786
Oct 26, 1786
43
Apr 11, 1787
May 20, 1787
6
Nov 25, 1788
Dec 29, 1788
20
Nov 25, 1788
Messier
Jan 3, 1789
Jan 6, 1789
2
Dec 21, 1788
C. Herschel
1
Jan 7, 1790
C. Herschel
Méchain
1787
Messier
1788I
Jan 19, 1786
Jan 19, 1790 P/Tuttle
Messier
Messier
1790II
1793I
1798I
Méchain C. Herschel
Apr 10, 1787
Méchain
Jan 10, 1790
?
7
Jan 9, 1790
Méchain
May 1, 1790
Jun 9, 1790
45
Apr 17, 1790
C. Herschel
Dec 26, 1791
Jan 28, 1792
12
Dec 15, 1791
C. Herschel
Feb 1, 1793
Feb 14, 1793
6
Jan 10, 1793
Gregory, Méchain
Sep 27, 1793
Dec 8, 1793
25
Sep 24, 1793
Perny
Sep 27, 1793
Messier
Aug 14, 1797
Bouvard
Sep 27, 1793
Jan 7, 1794
Aug 16, 1797
Aug 30, 1797
13
Apr 12, 1798
May 24, 1798
27
Apr 12, 1798
Messier
Dec 7, 1798
Dec 12, 1798
4
Dec 6, 1798
Bouvard
Méchain
1799I
Aug 10, 1799
Oct 25, 1799
44
Aug 7, 1799
Méchain
Méchain
1799II
Dec 28, 1799
Jan 6, 1800
5
Dec 26, 1799
Méchain
Pons
1801
Jul 12,1801
Jul 21, 1801
5
Jul 12, 1801
Pons, Messier, Méchain, Bouvard
Aug 30, 1802
Sep 5, 1802
7
Aug 26. 1802
Pons
Mar 11, 1804
Mar 17, 1804
6
Mar 7. 3. 1804
Pons
adopted from: Philbert, J.P.: Charles Messier – le furet des comètes
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The competitor: Johann Elert Bode Messier not only reinvented comet hunting, he blication of Messier’s first catalog of 45 nebulae, also sparked new interest with his contemporariBode started his own search for new nebulae and es in the observation of nebulae and star clustar clusters. He succeeded with some genuine sters. The German astronomer Johann Elert Bode discoveries (M 81, M 82, M 53, M 92) and a larger (1747–1826), who like Messier published an number of independent findings. In 1777, he comannual almanac, entered into a direct competitipiled his “Complete Catalog of all Observed Nebuon with the French astronomer in 1777, by prelae and Star Clusters,” based on his own observasenting his own catalog of nebulous objects. tions as well as on all references he could find in Bode developed an interest in astronomy at a the literature. At its time the largest deep-sky cayoung age. He observed the night sky from a talog, this included 75 objects. Bode continued to hatch in the roof of his parents’ house in Hamobserve, and he always encouraged other obserburg. By chance, a math professor saw Bode’s vers to publish their data in his almanac. The 1779 notes and encouraged him volume contains a listing of to write a popular astronoobjects found by Köhler from my book. In 1768 at just 21 Dresden, and other editions years old, Bode published reproduced the notes of the guidebook “Deutliche Oriani and a translation of Anleitung zur Kenntnis des Messier’s catalog. gestirnten Himmels” (“ConAn updated and enlarged list cise manual to the knowof contemporary observaledge of the starry sky”), tions of nebulae, still wiwhich was received very thout knowledge of Messier’s well and reprinted several third catalog version but times. A later edition was including the 68 objects of used to publish the formula his second, was published for the distances of the plaby Bode in 1782 within the nets, which was soon known “Vorstellung der Gestirne.” as the “Titius-Bode-Law.” This list not only included Still an amateur astronomer, several new discoveries, preBode observed the Venus sumably made by Bode himtransit of 1769. But in 1772, self, but also the objects IC he began to work at the Johann Elert Bode 4665 (already mentioned by royal observatory of Berlin, Al Sufi) and h & F Persei. and a few years later, in Despite the substantial work 1779, Bode discovered his first comet. Much like of Bode in this field, his name is hardly known Messier, that discovery gave him recognition. He today, by contrast to popular Messier. One good eventually became the director of Berlin Obserreason may be that Bode did not check the posivatory in 1787 and kept that office for 38 years. tions of objects contributed from other observers. Bode gained some fame as the founder of the That caused many errors in his list. His listing of “Berliner Astronomisches Jahrbuch” (“Berlin Astro- 1782, for example, contains three different entries nomical Almanac”) and with his book “Vorstellung for M 8, because Bode did not realize that the difder Gestirne” (“Introduction to the Constellations,” ferent positions from Messier, Le Gentil, and Köh1782) and the monumental celestial atlas “Uraler all referred to the same object. Hence, despite nographia” (1801). By contrast to Messier, Bode Bode’s strive for completeness, Messier’s final cawas well connected in scientific circles. The name talog of 1781 was, at its time, second to none in “Uranus” for the new planet discovered by William terms of quality. Herschel was his suggestion. And as director of the Berlin Observatory, he had excellent contacts all over Europe. In 1774, three years after the pu-
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The 13th of March in that same year saw the discovery of the planet Uranus by William Herschel in England. At first, Herschel took his new object for a possible comet and asked Charles Messier for his opinion. The same day he received Herschel’s letter, Messier observed Uranus. Messier passed his positional measurements down to de Saron to calculate the orbit. His mathematical friend was quick to realize that Uranus was not a comet but a new planet. After 1781, Herschel would find over 2000 new nebulous objects with his much better telescopes. However it was not only this superior competition that stopped Messier working on nebulae, but also another blow of fate: on the 6th of November 1781, Messier was on a walk with his family in the Park Monceaux. His curiosity led him to inspect the entrance to a basement, when he slipped and fell 8 m (24 feet) into a deep ice-storage cellar. Messier was seriously injured, and had broken his upper leg, upper arm, two ribs and the wrist of his hand. He lost a lot of blood from an open wound over his eye. It took him the better part of 1782 to recover from this bad accident. His leg had to be broken again, after the bones had healed at an angle. Messier was bed-bound for a long time, and he always limped thereafter. Herschel, who paid him a personal visit in Paris 20 years later, remarked that Messier never fully recovered from that injury. It was a full year after that accident before Messier was back in his observatory, on the occasion of the Mercury transit of the 12th of November 1782.
1789 to 1804: In the turmoil of the French Revolution The French Revolution began with the storming of the Bastille in Paris on the 14th of July 1789. As for so many, the following years brought chaos and insecurity to Messier. The structures of the French Navy were dissolved
and maintenance of the observatory ceased. Frequently, Messier had to borrow oil for his observing lamp from his good colleague Lalande. The latter was now director of the former Royal Observatory of Paris, and they knew each other well from the days when they both taught at the Collège Royal. In 1793, by decree of the revolutionary directorate, all academies were dissolved, with serious consequences for Messier. A further tragic event for Messier was to follow on the 20th of April 1794 when his good friend and benefactor de Saron was guillotined under the reign of terror. Already in prison, he calculated his last comet orbit for Messier. Fundamental changes were also imposed upon Lorraine. In 1793, the dukedom of Salm became part of revolutionized France by annexation, with significant consequences for the Messier family, which was closely involved with the local nobility. Some family members emigrated from France to Germany, following the dukes of Salm.
In 1795, a new astronomical institute was founded in Paris: the Bureau des Longitudes. Its original purpose was to outstrip the superiority of the English clocks. Messier was not among its founding members, like Méchain or Cassini, but he replaced the latter in the next year. In 1798, still living in the Hôtel de Cluny, Messier was on his own again, after the death of his sister in the previous year. From Senones, his younger brother and his niece Josephine now came to live with him. Josephine would take care of Charles Messier until his death. In 1801, Messier made his last comet discovery at the age of 71. Thereafter, he just lived off his past fame, which was finally recognized by the new regime. Napoleon personally bestowed him with the Cross of the Legion of Honour. This led Messier to make, in 1808, a connection between his discovery of the great comet of 1769 and the simultaneous birth of “the Napoleon the Great.” This idea was so close to astrology that it did not go over well with most contemporary astronomers.
The colleague: Pierre Méchain Thirty of the now so-called “Messier objects’’ were, in fact, discovered by Pierre Méchain (1744–1804). He was a close collaborator of Messier and helped complete his final catalog in the years 1779 to 1781. Pierre Méchain was born in Laon. He planned to become an architect, but lack of finances forced him to abandon his studies. Rumour has it that he even had to sell his telescope, which he had bought as an amateur astronomer, and that the buyer turned out to be Jérôme de Lalande, later (1794) to become the director of Paris observatory. Lalande had been astronomy professor at the Collège Royal from 1760 to 1767, as the successor of Delisle, and from 1794 to 1807 he was also editor-in-chief of the Connaissance des Temps. In 1772, he managed to get Méchain a job at the treasury of the French Navy in Versailles. Two years later, Méchain obtained the official position of a “calculator.” The connection with Messier’s friend Lalande initiated Méchain’s contribution to the Messier catalog. In 1781, Méchain found two new comets – eventually, his total score grew to eight discoveries. Unlike Messier, he was able to calculate his own orbits. His most famous discovery was the comet of 1786, which was proved by Encke’s orbital calculations to be the secondknown periodic comet (after Comet Halley).
From 1786 on, Méchain was engaged in longitude measurements. This work requires clocks much more accurate than those available at the time – a big problem for offshore navigation, as well as for geodesy on land. Hence, in 1791, the French Academy of Sciences started a project to define the French prime meridian from Dunkirk in the north to Barcelona in the south. After the project finished in 1795, Méchain found an error of 3" in the calculated latitude of Barcelona (about 90 meters on the ground). We know now that this was due to a combination of instrumental inaccuracies and some deviation of the globe from a perfect sphere – but Méchain expended considerable effort trying to further increase the Pierre Méchain, painted by Hurle. accuracy of the calculations. In 1798, he succeeded Lalande as director of the Observatory of Paris. In an, Méchain contracted yellow fever and died on the 20th of September 1804. 1804, during field work in Spain to revise the measurements along the French prime meridi-
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Portrait of the comet hunter from 1801, at the age of 71, drawn by Cless from Weimar. Messier was reasonably tall for his time, measuring 1.68m (5 feet 6 inches), a little chubby, and his hair turned white around the age of 60.
The last comet that Messier was able to observe was the great comet of 1807. Thereafter, he suffered from failing eyesight. After 1808, he could no longer read or write. In 1812, he became paralyzed on one side, and dropsy set in around 1815. Messier finally died on the 11th of April 1817 at the age of 87 years. Three days later, he was buried in the cemetery of Père Lachaise. The speech at Messier’s grave was given by Delambre, secretary of the reconstituted Royal Academy of Sciences. He commemorated the comet hunter with the words: “He did not write a single book, nor any treatise in general or in particular, but his observations will for a long time enrich the collection of the Academy. His famous colleague Lalande has created a constellation in his honor, the only one bearing the name of an astronomer. It will keep the memory of him alive, but his name will remain with science, independent of this honouring act of friendship: in terms of the catalog of comets, in which the name Messier has been recorded as often as honestly.”
William Herschel continued with Messier’s work. Painting by Contel, from an engraving.
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The Observations
Work on the catalog M 1 and M 2: Beginnings and motivation Charles Messier’s first encounter with a nebulous object occurred during his preparations for the return of Comet Halley. When he observed Comet de la Nux for that purpose in August 1758, he came across an object in Taurus, which looked very similar to the comet, but it did not move. It was the 28th of August 1758 when Messier discovered the Crab Nebula, now known as M 1. He obtained the position of this apparently new nebula two weeks later (12th of September ). Messier did not know then that M 1 had already been found by Charles Bevis in England in 1731, and so took his observation for a new discovery. That kindled an interest that would eventually lead to his famous catalog. As he described it in 1801: What made me produce this catalog was the nebula which I had seen in Taurus, September 12, 1758, while I was observing the comet of that year. The shape and brightness of that nebula reminded me so much of a comet, that I undertook to find more of its kind, to save astronomers from confusing these nebulae with comets. I continued to observe with telescopes suitable for the discovery of comets, which was the purpose I had in mind when producing this catalog. Messier did not start a systematic search straight away. However, it was two years before he found M 2, with a Gregorian reflector of 30-inch focal length and a power of 104×. Only later was he to learn, during a search for comet observations from other astronomers, that this object had already been discovered in 1746 by Jean-Dominique Maraldi (1709–1788). Again, Messier was not the original discoverer.
M 3 to M 40: Systematic search for nebulae In May 1764, Messier finally started systematic work on the catalog of nebulae. He began with the “nebulosae” in the lists and literature known to him, in particular those from Hevelius, Huygens, Derham, Halley, de Chéseaux (of which, apparently, he had only an incomplete knowledge), Lacaille, and Le Gentil. In addition, he discovered new objects of his own; some of these, like M 39 and M 40, while trying to verify entries from old catalogs. In only five months, Messier observed
and measured the positions of M 3 to M 40, including 19 genuine first discoveries. Hence, the first version of his catalog was more or less accomplished within half a year of work, from spring to fall 1764. That time must be considered the most productive phase in the life of Charles Messier as a “deep-sky observer,” as we would put it today, and it laid the foundation for his lasting popularity.
M 41 to M 45: Completion of the first catalog Early in 1765, Messier found the open cluster M 41. For a long time, this was the last entry in his observing log. The subsequent pause of four years saw his boat journey to the Netherlands in 1767 and further comet discoveries – apparently, Messier was pondering whether to publish his list of nebulae or not. In March 1769, he finally made up his mind and completed the catalog with the inclusion of several wellknown objects as his entries M 42, M 43, M 44, and M 45, listed under the date of the 4th of March 1769. All of these objects are impossible to confuse with a comet, and it remains a matter of speculation why he added them. Perhaps having a catalog with 41 objects did not satisfy Messier’s sense of symmetry, and he wanted to exceed the 42 entries in the catalog of his role-model, Lacaille. In his foreword, Messier mentioned the motivation for making a list of all nebulous patches in the sky, rather than just those which look like a comet. However, he did not include other significant objects in that respect, e.g., the double cluster h &F Persei, which apparently did not bother him much. There simply were not enough such objects left to round the number up to an even better sounding total of 50 entries. The manuscript for the first catalog was finally completed on the 16th of February 1771. It was printed in that same year for the 1774 edition of the Mémoires de l’Académie Royale des Sciences.
M 46 to M 52: Further discoveries Only three nights after the manuscript of the first catalog was finalized (19th of February 1771), Messier discovered four more objects: three more star clusters (M 46 to M 48) and the first galaxy of the Virgo cluster, M 49. Later that same year, on the 6th of June an object was discovered but its position not measured until 1779, which gave it a much later entry as number 62. Instead, on the 5th of April 1772, Messier finally found a nebula from a note of Cassini, for which he had been looking since 1764, now his M 50 – not much more than a week after his wife and newborn child had died.
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During an observation of the Andromeda Galaxy on the 10th of August 1773, Messier discovered the companion galaxy M 110. But for reasons that are not known, he did not include this object in his catalog. The observation and a drawing were finally published in 1798 – for this, M 110 was accepted as a Messier object in the twentieth century. Also in 1773, Messier came across M 51, while he was following the comet of that year which he had discovered himself. He saw only the central part of the main galaxy. The double-nature of this object was noticed later by Méchain, whom he got to know in that year (1773). M 52 in 1774 was then for some time Messier’s last discovery; he did not engage himself again with nebulous objects until 1777.
M 53 to M 70: Completion of the second catalog version In February 1777, Messier found M 53 and the faint M 54, and M 55 followed on the 24th of July 1778, while he was looking again for an object described by Lacaille (M 55), which he had failed to find in the night of the 29th of July 1764. Meanwhile, in 1777, Bode had entered into a direct competition with Messier with his catalog of 75 nebulous objects. Then in 1779, the 6th of January, the German challenged Messier in his very domain: Bode discovered his first comet. Messier saw it only 13 nights later. The comet then happened to pass near M 56, which Messier happily added to his list. Further nebulous objects were soon found along the path of Bode’s comet by different observers: M 57 on the 31st of January 1779 by Darquier, the Virgo galaxies M 59 and M 60 on the 11th of April by Köhler (four days later independently discovered by Messier, together with M 58), and M 61 by Oriani, on the 5th of May. The latter galaxy was seen by Messier the same night, but confused with the comet; he noticed his mistake six nights later. The other galaxies of the Virgo cluster had not yet been observed. June 1779 saw the first contribution to the Messier catalog by a discovery of Méchain: M 63. In March and April 1780, Messier had a very productive phase again: he discovered M 64, M 65, M 66, M 67, and M 68. The much grown number now motivated him to publish a second version of his catalog. It was printed in the 1783 edition of the French Almanac, the Connaissance des Temps. Two more objects (M 69 and M 70) found by Messier on the 31st of August 1780, and making a pleasantly round number, were added on in the annex of the same edition.
M 71 to M 103: Méchain’s discoveries and the final catalog version Again, new discoveries were made immediately after the publication of the catalog. More than 32 new objects were observed between October 1780 and March 1781. The personal discoveries achieved by Messier were M 73 (when he was looking for M 72 of Méchain), M 84, M 86, and M 87 to M 93
26
Observations of nebulae before Messier For the earliest astronomers, nonstellar (fixed) objects had little importance and hardly any attention was paid to them. The only exception was the easily resolved and bright star cluster of the Pleiades, which played an important role in astronomical calendars and mythology. For example, the tradition of All Saints Day and Halloween is based on the culmination time of the Pleiades. Nebulae were not noticed by the ancient Greek scholars, only Hipparchus mentioned, apart from the Pleiades, the other two cloud-like objects, M 44 and h & F Persei. The great star catalog of the second century AD, the Almagest produced by Ptolemy (83–161), already contained seven objects characterized as “cloud-like” or “nebulous.” But apart from M 7, M 44, and h & F Persei, they are not real but rather chance alignments of stars that remain unresolved and therefore appear nebulous to the naked eye. Not even the two most obvious of the real nebulae, M 31 and M 42, are mentioned in the Almagest, nor elsewhere in antiquity. This demonstrates the lack of interest in such objects. The first note on M 31 came from the Persian scholar Al Sufi in the tenth century, when he worked on a revision of the Almagest. And the discovery of M 42 had to wait until the first telescopic observations in the early seventeenth century. In 1611, several astronomers discovered the Orion Nebula almost at the same time – the very first of them was Nicholas Peiresc. The first telescopes were also used for several other non-stellar objects. Galileo found that M 44 was not a nebula but a cluster of faint stars. About the same time, Simon Marius discovered M 31, which was still
unknown in Europe. After him, Giovanni Batista Hodierna (1597–1660) made a series of discoveries. His list of 19 observed objects contains nine genuine discoveries (including M 6, M 36, M 37, M 38, M 41, M 47, and perhaps M 33, and M 34), but his notes were lost and remained entirely unknown until their rediscovery in the twentieth century. For quite some time not much progress was made; nebulae were still objects of little interest. In 1647, Johannes Hevelius published one of the last large star catalogs achieved without the use of a telescope, he therein mentioned 14 “nebulous” objects, mostly taken from Ptolemy. As in the Almagest, these “nebulae” are mostly accidental stellar patterns, which are not resolved by the naked eye. However, with the advent of this widely known publication, nebulous objects gained a bit more attention for the next hundred years. In 1733, Hevelius’ original listing of 14 objects was translated from Latin into English by William Derham and supplemented with M 7 and NGC 6231. In this form, it came to Charles Messier, who tried to verify these 16 objects in 1764. Since most of them were not real, they could not be identified as a nebula through the telescope. Only Hevelius No. 14 survived as M 40, as Messier included it in his catalog, although he only saw a faint double star and no nebulous object. Not long after the work of Hevelius, M 22 (Ihle, 1665) and M 11 (Kirch, 1681) were found by telescopic observation, the first discoveries made from Germany. In England, meanwhile, Edmond Halley was quite active. Best known for his long-period comet, he had already discovered Z Cen in the southern sky in 1677. From
home, he found M 13 in 1714. In a 1715 publication, he also described M 42, M 31, M 22, and M 11. But it wasn’t until Messier’s time, when the quality of telescopes had improved sufficiently, that more progress could be made. In 1746, the Swiss aristocrat de Chéseaux (1718–1751) listed 21 observed nebulae, which include eight genuine discoveries. But as in the case of Hodierna, his notes were not published, because de Chéseaux was not a member of any important scientific society, so he was not accepted by the scientific establishment. This was different with Nicolas Louis de Lacaille (1713–1762), who presented a list of 42 nebulous objects in 1755 as a byproduct of his star survey of the southern sky. Despite the very small aperture he had used, this first real nebula catalog contained a significant number of genuine discoveries and was of very good quality, especially in terms of positional information. Certainly, it was the best example for Messier, who reprinted Lacaille’s list as an annex to his 1771 catalog. Hence, many southern objects were known before Messier’s work, while the northern sky was still almost untouched. Concurrently with Messier, Guillaume Le Gentil (1725–1792) made a few discoveries. Like Messier, he once was a student of Delisle in the Collège de France. In his publication, submitted in 1749 but not printed until 1755, Le Gentil mentioned M 32, M 8, M 41, M 36, and M 38.
Some astronomers who paved the way for Messier: Hevelius, Flamsteed, Halley, Peiresc, de Mairan, Huygens.
Hevelius “Nebulosae,” 1647 Derham’s number
Constellation Derham’s description
Modern identification
1
Andromeda
In Andromeda’s girdle
M 31
2
Cancer
Praesepe
M 44
3
Capricornus
In the forehead of Capricorn
V Cap
4
Capricornus
Another, preceding the eye of Capricorn
S Cap
5
Capricornus
Another following it
R Cap
6
Cygnus
Preceding above the Swan’s tail and last in its northern foot
Z Cyg
7
Cygnus
One of two following the Swan’s tail, outside the constellation
?
8
Hercules
At the tip of Hercules’ left foot
88 Her
9
Hercules
In the left leg of Hercules
90 Her
10
Hercules
In the head of Hercules
32, 33, 34 Oph
11
Libra
Under the beam of the western scale
], 17, 18 Lib
12
Pegasus
Following the ear of Pegasus
34, 35, 37 Peg
13
Scutum
Below the western border of the shield
?
14
Ursa Major
Above the back of Ursa Major
?
27
Visual observers after Messier From the seventeenth to the nineteenth century, visual observation at the telescope’s eyepiece was the common scientific means of documentation in astronomy. The observers would produce drawings and descriptions, which were then reproduced in professional publications. It was not until the end of the nineteenth century that emerging photographic techniques evidently became the more accurate and less subjective form of recording positions and intensities than visual observation. Nevertheless, descriptions from the great historic visual observers are still most valuable for the modern amateur for comparison with his or her own visual observations. We have to keep in mind that those historic observers could not “cheat” and look at a photograph to get some help; they depended entirely on the capabilities of their eyesight.
Frederick William Herschel (1738–1822) William Herschel was a musician, born in the German town of Hanover, who had emigrated to England. He became the first observer to undertake a systematic search for nebulae for their own sake. Most likely, he was inspired by Messier’s catalog. Within 20 years, he compiled a huge catalog of 2500 nebulae and star clusters. Herschel had produced home-made telescopes and mirrors since 1774, for himself as well as for other astronomers. For his nebula observations, which he started in 1782, he used a very large, modified Newtonian telescope with 18 inches (475mm) of aperture and 20-feet (6m) focal length. His standard magnification was 157× with a field of view of 15', with which he was systematically scanning the sky. He combed through a zone of 4 minutes to 5 minutes in right ascension with a length of 12° to 14° in declination and noted all newly
28
found objects for a later, accurate position measurement. This procedure was then repeated in a band of right ascension adjacent to the preceding field. Wanting a larger objective for this project, Herschel finished building the then largest telescope in the world in 1789, with a huge 47-inch (1.2m) metal mirror of 40-feet (12m) focal length, but it proved too bulky for scanning purposes, so he would instead use it for detailed observations of individual objects. Herschel’s first discovery, on the 7th of September 1782, was the Saturn Nebula NGC 7009. By 1785, he had found about 1000 more nebulous objects, another 1000 by 1789, and a final 500 by 1802. Hence, his 20 years of work increased the number of known nebulae by a factor of more than 20 – an immense achievement. William Herschel is probably the most industrious deep-sky observer of all time.
and the revised observations of his father into the General Catalogue (GC) of Nebulae and Star Clusters. It became the basis for the famous New General Catalogue (NGC) of 7840 entries. The latter, created by Johann Dreyer in 1888, included all the objects then known and is still in widespread use today.
William Smyth (1788–1865) The retired English admiral discovered astronomy as his hobby and built his own private observatory with a 6-inch refractor. In close contact with John Herschel, he observed numerous deep-sky objects. In 1844, he published the “Bedford Catalogue,” the “grandmother” of all deep-sky observing guides, which included descriptions of 98 nebulae and 72 star clusters. His work offers rich insights into the practice of amateur astronomy 160 years ago.
John Herschel (1792–1871)
William Lassell (1799–1880)
John diligently continued the work of his father. He shipped the venerable 18-inch telescope to South Africa, where he systematically searched the southern sky for nebulae. In the years 1834 to 1838, he discovered 1689 new objects. In 1864, he finally combined his own
This wealthy brewer and amateur astronomer from Liverpool, England, was able to spend considerably more money for his astronomical desires than his contemporaries. In 1845, he built a 24-inch Newtonian on a fork-mount, which he used to do numerous observations and drawings of nebulae. In 1858 in Liverpool, he had a reflec-
tor with a 48-inch mirror made, one of the largest telescopes of its time. He shipped it to Malta in 1861, to take advantage of the far superior observing conditions there.
William Parsons, Lord Rosse (1800–1867) The third Earl of Rosse was a rich Irish nobleman who developed an enthusiasm for observing due to his contact with John Herschel. In April 1845, after considerable experimentation with the techniques needed to build very large reflectors, he constructed his huge telescope, “Leviathan,” which had a 72-inch (1.8m) mirror. Then the largest telescope in the world, it was set up in the gardens of his Irish estate at Birr castle and was so cumbersome that several people were required to operate it. Nevertheless, the Lord himself and several assistants made a large number of observations and drawings of nebulae in the decades to follow. One of his most important discoveries was the spiral structure of some galaxies. However, this success later tricked him into seeing spiral patterns even in star clusters. The assistants of Lord Rosse were: J. Rambaut (1848), B. Stoney (1850–1852), R. Mitchell (1853–1858), S. Hunter (1860–1864), S. Ball (1866–1867), C.E. Burton (1868–1869), R. Copeland (1871–1874), J. Dreyer (1874–1878).
Heinrich d’Arrest (1822–1875)
Leo Brenner (1855–1936)
D’Arrest, a descendent of Huguenot immigrants to Germany, was director of the Copenhagen Observatory near the Danish capital. His published notes, “Siderosum Nebulorosum,” which contain observations of 1942 objects and include 321 discoveries, prove that he was a very diligent observer. For most of his work, he used the 11-inch refractor at the Copenhagen observatory.
Spiridon Gopþeviü is one of the most debated observers of all time. In 1894, he started to approach the public under his pseudonym Leo Brenner. On the Mediterranean island of Lussin, which then belonged to Austria (today the Croatian island Lošinj), he built a private observatory with a 7-inch refractor and published many incredibly detailed, but often fictitious, reports. In 1909, after he had lost almost all his credibility with professional astronomers, he simply vanished from the astronomical scene. His descriptions are relevant for the German-speaking community, though, because in 1902 he published the first ever observing guide on the deep-sky in the German language.
Léopold Trouvelot (1827–1895) This French painter received considerable recognition for his precise drawings of plants and animals. His sketches of the aurora borealis finally caught the attention of Harvard astronomers in Cambridge (USA), who invited him to hone his talents with telescopic observation. In 1875, he was hired by the US Naval Observatory in Washington (DC), where he subsequently produced more than 7000 drawings of astronomical objects – still the finest of their kind. However, after his death, Trouvelot acquired a bad reputation in the USA because he introduced the European gypsy moth, whose caterpillars have caused a lot of damage to US agriculture ever since.
Wilhelm Tempel (1821–1889) With a very humble, provincial family background in the east of Germany, he received his first recognition from abroad. His breakthrough came in 1859 when he discovered a comet and the nebula in the Pleiades that surrounds Merope – both feats were achieved with his small 4-inch refractor. In 1874, Tempel started work at the Arcetri Observatory near Florence (Italy), where he carried out numerous observations of nebulae and made 146 discoveries of new objects.
Edward Emerson Barnard (1857– 1923) This American is regarded as perhaps the best visual observer of all times. He had the combined gift of a keen eye and a well-trained, accurate perception. Coming from a very poor family background, Barnard started his career as a laboratory assistant in a photography shop and observed the night sky as an amateur astronomer. He soon became known as the discoverer of several comets. In 1887, he was hired by the Lick Observatory, where he made some spectacular discoveries with the 36-inch refractor, then the largest refractor in the world. Apart from his skills as a visual observer, he was also a very successful pioneer of deep-sky astrophotography.
29
Star chart with the observed path of the comet of 1764, according to Messier’s positional measurements.
– all other new objects were contributed by Méchain, but verified by Messier through observation and positional measurement. The last version of the catalog was supposed to have the round number of 100 entries. However, Méchain was discovering new objects in such quick succession, that Messier could not verify them all in time for the submission deadline of the manuscript. Hence, he added M 101, M 102, and M 103 to the finalized list with the remark: “From M. Méchain, have not yet been observed by M. Messier.” The objects M 108 and M 109 had been mentioned only in the note on M 97. Apparently, this third version of the catalog was prepared under considerable time pressure. It was printed already in spring 1781, for the 1784 edition of the Connaissance des Temps.
30
M 104 to M 109: After press Shortly after he received his personal copy of the third catalog from the printer, Messier made a hand-written note in it about a further discovery of Méchain's from the 11th of May 1781: M 104. Messier also added positions for the now-measured objects M 102 and M 103, as well as for M 108 and M 109 (in the note on M 97). Hence, initially, there was no indication that this would be the last version of Messier’s catalog. Also, Méchain remained active. Not only did he discover his first two bright comets on the 28th of June and the 9th of October of 1781, in July he also discovered the nebula now known as M 106. In addition, a discovery made by Méchain in March that year, M 105, had simply been overlooked in those final hectic days of work on the catalog. The next year (April 1782), M 107 was found by Méchain. Nevertheless, a new, updated version of the Messier catalog would never come. That may well be “blamed” on William Herschel.
De Chéseaux’s list of nebulae Philippe Loys de Chéseaux was a rich, Swiss nobleman living in the countryside near Lausanne, where he had his own observatory. He became known as a result of his independent discovery of comet Klinkenberg (C/1743 X1), on the 13th of December 1743. On the 13th of August 1796, he discovered another comet, C/1746 P1. Using a 2-foot (focal length) Gregorian reflector, he drew up a list of 21 star clusters and nebulae in 1746. For eight of those objects (M 4, M 16, M 17, M 25, M 35, M 71, NGC 6633, and IC 4665), he is the original discoverer.
He sent his list to his grandfather Reaumur, who was a member of the French Academy of Sciences, and who presented the list at an Academy meeting on the 6th of August, 1746. However, no printed publication followed, and de Chéseaux’s work was forgotten until its rediscovery in 1884. Messier mentioned the list in the foreword to his first catalog version, but apparently, he had no complete knowledge of it.
Star clusters: 1. M 6
Between Scorpius, Ophiuchus, and Sagittarius, there is a very beautiful one, of which the principal stars have this year RA 260° 52' 30" and southern declination 32° 1' 30". 2. IC 4665 Above the shoulder, beta of Ophiuchus, a cluster of stars of which the two principal stars have this year: RA 264° 46' 50" and southern [should read northern] dec. 6° 50' 20"; RA 264° 31' 55" and southern [should read northern] dec. 7° 00' 10". 3. NGC 6633 Near the tail of Serpens in which there is a small cluster of stars, a bit separated from the rest to the west; its RA is at 273° 32' 30" and its southern [should read northern] declination is 6° 19' 20". 4. M 16 A cluster of stars between the constellations of Ophiuchus, Sagittarius, and Antinous, of which RA is 271° 3' 10" and southern declination is 13° 47' 20". 5. M 25 Another [star cluster] between the bow and the head of Sagittarius, of which RA is about 274° 17' and southern decl. is 19° 11' 30". 6. NGC 869 7. NGC 884 Two clusters of stars in the hilt of Perseus’ sword, earlier observed by M. Flamsteed. 8. M 8 Another [star cluster] in the bow of Sagittarius, observed by the same. 9. NGC 6231 10. M 7 The last two [objects] of the catalogs of Messieurs Derham and Maupertuis. 11. M 44 That in Cancer, ordinarily called Praesepe, the position of which is known. 12. M 35 13. M 71 Two others of which I have not yet determined the positions, one above the northern feet of Gemini, and the other below and very close to Sagitta. 14. M 11 Lastly, a prodigious cluster of small stars, near one of the feet of Antinous of which RA is 279° 21' 10" and southern decl. is 6° 32' 20"; it has about 4 1/8' in diameter. These 14 nebulae contain among them almost as many stars visible in telescopes of 25 feet as the greater part of the sky contains as visible to the naked eye. Here now are the rightly styled nebulae which, when seen in the largest telescopes, never appear as anything but white clouds: 17. M 22 A third, discovered by Abraham Ihle, between the head and the bow of Sagittarius, of which I found the RA of 275° 14' 10" and southern dec. 24° 5' 30". It is 5' in diameter, it is round, of a reddish color, whereas the Andromeda Nebula is yellowish and that of Orion, transparent. 18. NGC 5139 That in Centaurus, discovered by Mr. Halley; it is invisible in Europe. 19. M 4 One which is close to Antares, of which I have found for this year, RA 242° 1' 45" and southern dec. 25° 23' 30". It is white, round and smaller than the preceding ones; I do not think it has been found before. 20. M 17 Lastly, one other nebula, which has never been observed. It has a shape quite different from the others: it has the perfect form of a ray, or of the tail of a comet, 7' long and 2' wide; its sides are exactly parallel and quite well terminated, the same for the two ends. The center is whiter than the edges. I found its RA for this year as 271° 32' 35" and its southern declination as 16° 15' 6". It makes an angle of 30° with the meridian. 21. M 13 I have not yet found that in Hercules, discovered by M. Halley. I very much hope that the Messieurs astronomers of Paris will be willing to indicate its position for me.
31
The catalog of Abbé Lacaille No.
Present designation
Con.
R.A.
Tuc
0h 33.41min
Decl.
Pos.-error
Type
–72° 4'
41'
GC
First section: Nebulae without stars Lac I.1
NGC 104
h
min
Lac I.2
NGC 2070
Dor
5 38.4
–69° 10'
5'
GN
Lac I.3
NGC 2477
Pup
7h 50.9min
–38° 37'
15'
OC
min
h
Lac I.4
NGC 4833
Mus
12 59.7
–70° 49'
4'
GC
Lac I.5
NGC 5139
Cen
13h 26.8min
–47° 29'
0'
GC
Lac I.6
M 83
Hya
h
min
–29° 52'
2'
Gx
h
min
–62° 56'
1'
OC
–40° 39'
0'
OC
min
13 37.1
Lac I.7
NGC 5281
Cen
13 46.6
Lac I.8
NGC 6124
Sco
16h 25.6min h
Lac I.9
M4
Sco
16 23.7
–26° 31'
2'
GC
Lac I.10
NGC 6242
Sco
16h 55.6min
–39° 28'
0'
OC
min
h
Lac I.11
M 69
Sgr
18 30.0
–33° 29'
1,2°
GC
Lac I.12
M 22
Sgr
18h 36.4min
–23° 55'
1'
GC
min
h
Lac I.13
(NGC 6777)
Pav
19 26.8
–71° 30'
2'
Ast
Lac I.14
M 55
Sgr
19h 40.1min
–30° 57'
2'
GC
Hor
4h 3.0min
Lacaille’s catalog of nebulae It seems astounding that the very first catalog of deepsky objects, presented in 1755 by Abbé Nicholas-Louis de Lacaille – 14 years before Messier’s first catalog of 45 objects – was actually devoted to the southern sky. In any case, Lacaille’s catalog was the first significant work of its kind, which also became widely known and accepted. Earlier object lists either had been very short (like the one by Halley), or had not reached the wider scientific community (like those of Hodierna in 1654, or de Chéseaux in 1746). Lacaille’s catalog of 42 objects was published in 1755 in the Memoirs of the French Academy of Sciences, and again in 1784 as an annex to Messier’s work. Lacaille’s
Second section: Star clusters Lac II.1 Lac II.2
Collinder 140
CMa
–44° 28'
0'
Ast
h
min
–34° 09'
2,1°
OC
h
min
7 26.2
Lac II.3
NGC 2516
Car
7 58.9
–60° 50'
9'
OC
Lac II.4
NGC 2546
Pup
8h 11.2min
–37° 13'
28'
OC
h
min
Lac II.5
IC 2391
Vel
8 38.8
–53° 6'
17'
OC
Lac II.6
Collinder 203
Vel
8h 46.8min
–42° 16'
19'
OC
min
–51° 43'
2'
OC
–58° 13'
2'
OC
h
Lac II.7
NGC 3228
Vel
10 21.4
Lac II.8
NGC 3293
Car
10h 35.9min h
min
Lac II.9
IC 2602
Car
10 43.1
Lac II.10
NGC 3532
Car
11h 6.5min
Lac II.11
-
h
Cen
11 22 h
min
–64° 24'
1' (37")
OC
–58° 40'
10'
OC
–58° 21'
2'
Ast
min
Lac II.12
NGC 4755
Cru
12 53.7
–60° 22'
1'
OC
Lac II.13
NGC 6231
Sco
16h 54.2min
–41° 50'
1'
OC
3'
OC
Lac II.14
M7
h
min
Sco
17 53.8
–34° 45'
Third section: Stars with nebulosity Lac III.1
nonexistent
Pic
5h 3.4min
–49° 30'
Lac III.2
NGC 2547
Vel
8h 10.7min
–49° 15'
7'
OC
Lac III.3
IC 2395
Vel
8h 42.4min
–48° 6'
2'
OC
–57° 0'
4'
OC
Lac III.4
IC 2488
Vel
h
min
9 27.8 h
min
Single star
Lac III.5
Collinder 228
Car
10 44.0
–60° 7'
3'
OC
Lac III.6
NGC 3372
Car
10h 44.3min
–59° 30'
10'
GN
Lac III.7
NGC 3766
Cen
11h 36.2min
–61° 37'
0'
OC
Lac III.8
NGC 5662
Cen
14h 35.3min
–56° 34'
4'
OC
h
min
Lac III.9
-
Cir
15 22.7
–59° 10'
2'
Ast
Lac III.10
NGC 6025
TrA
16h 3.8min
–60° 30'
5'
OC
min
h
Lac III.11
NGC 6397
Ara
17 40.7
–53° 42'
2'
GC
Lac III.12
M6
Sco
17h 40.1min
–32° 13'
3'
OC
–24° 22'
1'
OC+GN
–56° 53'
1'
Ast
Lac III.13 Lac III.14
M8 -
Sgr Ind
h
min
18 3.9 h
21 31.1
min
Ast = asterism. The coordinates are the positions given by Lacaille as for equinox 2000.0.
32
1' (52")
The frontispiece of Lacaille’s catalog depicts a contemporary view of the Paris Observatory.
list has three sections: “Nebulae without Stars,” “Star Clusters,” and “Stars with Nebulosity.” Incidentally, each of the sections contains exactly 14 objects. This equipartition already puzzled Kenneth Glyn Jones in the 1960s. Perhaps it satisfied a baroque desire for symmetry. Lacaille himself remarked on his list as follows: “I have found a large number of nebulae of these three types in the southern sky, but I would not believe that I have noticed all of them; in particular of the first and third type, because these are visible only after dusk and in the absence of the Moon. Nevertheless, I hope that this list is more or less complete for the most remarkable objects of the three types.” For his task, Lacaille had only very humble optical equipment. He wrote: “I have wished dearly to present a more detailed and informative work. But the simple refractors available to me at the Cape of Good Hope, of 15 and 18 inches [focal length], were neither adequate nor sufficient for this kind of observation.” Since his telescopes were probably non-achromatic with focal ratios of around f/10, their apertures cannot have exceeded 40mm (1½ inches). The fact that Lacaille could not resolve ZCentauri (NGC 5139) into individual stars, or open clusters like NGC 6124, reveals the poor quality of his instruments.
Messier’s drawing of M 42, published in the annex of the first catalog. For this observation, Messier used an achromatic Dollondrefractor with an aperture of 40 lines (90mm), a focal length of 3.5 feet (1.14m), and a magnification of 68×, on the nights of the 25th and 26th of February, and the 19th, 23rd, 25th, and 26th of March 1771. The circular border represents the edge of the actual field of view, about 30'. South is above.
The German-born musician, who had emigrated from Hanover to England, became famous for a discovery he made on the night of the 13th of March 1781 – only four days after the last official entry to Messier’s catalog. At first, Herschel took his new object for a comet, and so he asked Messier, the famous expert on comets, for his opinion. Messier observed the new object, measured its position over several nights, and had his friend de Saron calculate the orbit. The result was sensational: Herschel had found a new planet, Uranus. With the fame of this discovery, Herschel received a royal salary, which finally allowed him to concentrate fully on astronomical work. In 1782, he began an extensive search for new nebulous objects and, due to both his superior Newtonian telescopes and his dedication, made about 1000 new discoveries by 1786. By the end of that project in 1802, Herschel had compiled a huge list of about 2500 nebulae. It was the Messier catalog (he received his copy on the 7th of December 1781) that almost certainly gave him the idea. At the same time, the unlucky Messier had to abandon all his work after his serious accident (6th
of November 1781). After a long, painful recovery, he did not resume his search for new nebulae – in 1802 he described why: After me, the famous Herschel published a catalog of 2000 [nebulae] which he had observed. Unveiling the sky in his way, with instruments of large aperture, is not useful for comet seeking. Hence, my objective is different from his: I only need the nebulae that are visible in a telescope of 2 ft [focal length]. I have observed more, meanwhile. I will publish them in the future, organized by right ascension, for the sake of finding them more easily, and so that those who are looking for comets have less uncertainty. But such a final publication never came to be.
33
words. There is now broad consensus about most identities, except the case of M 102.
M 47
Examples of Messier’s observing results: a drawing of Saturn, the occultation of Saturn by the Moon on the 18th of February 1775, and the sunspots of the 17th of July 1777.
Messier’s position lies in a field without any recognizable star clusters. Hence, astronomers after Messier long believed that M 47 did not exist. However, in 1959, T.F. Morris was able to prove an assumption that Oswald Thomas made in 1934: Messier made a sign-related mistake in his calculation of the position. As a curious result, M 47 has two NGC entries: a false one, NGC 2478, in its wrong position, and the true one, NGC 2422, with the correct coordinates from Herschel.
M 48
The “missing” Messier objects Messier’s catalog was of high quality and contained relatively few errors. For each object, Messier took the position relative to a bright neighbor star. Furthermore, a large number of objects was observed more than once, especially for the third version of the catalog. Nevertheless, Messier could not entirely avoid making mistakes. Consequently, there are a few objects for which the identification remained ambiguous and matter of debate. Glyn Jones called these the “missing Messier objects,” which has become the adopted choice of
34
The same night he recorded M 47, Messier made another simple calculation mistake with M 48, putting it exactly 5° too far south. Again, Oswald Thomas and T.F. Morris found the right identity: NGC 2548 has now been commonly accepted as M 48.
M 91 With this galaxy, a positional error is also the most likely explanation. There is no sufficiently bright galaxy at the position given by Messier, only a lot of faint galaxies of the Virgo Cluster. Owen Gingerich suggested that M 91 may just be an accidentally repeated observation of M 58, a galaxy only 2.7° south of Messier’s position. But in 1969, W.C. Williams showed that Messier used a galaxy as his reference point for M 91 (there are hardly any bright stars in this field) and that he sim-
Bode’s catalog of nebulae In 1777, three years after Messier presented his first catalog, the Berlin astronomer Johann Elert Bode undertook the same endeavor. In his publication “On several newly discovered nebulous stars and a complete listing of all known so far” he wrote: “I wanted to search for nebulous stars [objects] with diligence. Since I had the pleasure to discover a number of new ones, which until then, at least, I had not found with any other astronomer, I herewith wish to communicate them.” With the use of several different sources, including Messier’s first catalog, Bode managed to collect 75 objects north of –35° declination. However, the diverse origin of the data was also the problem with Bode’s catalog. We only know with certainty of eleven objects that Bode observed himself. Of these, M 53, M 81, and M 82 were his own discoveries. All of the other objects had been copied from the literature without any verification, as Bode admits: “I have to add that I myself have not yet had the opportunity to observe all of the nebulae discovered by other astronomers.” As an example, this explains why M 8 has been listed three times – with different positions. The problem of non-verified entries was the death-sentence for Bode’s list, despite his good reputation as an astronomer. He printed it once again in 1782 in his star atlas “Vorstellung der Gestirne,” expanded with some new discoveries (including M 92, IC 4665, and the star pattern near F Dra known as the “little Cassiopeia”), but the catalog never achieved widespread international use.
The catalog of Johann Elert Bode
The catalog of Johann Elert Bode
Bode’s No.
Present designation
Original source
Bode’s No.
Present designation
Original source
1
?
own observation
39
M6
Lacaille
2
M 32
Messier
40
90 Her
Hevelius
3
M 31
Messier
41
M7
Lacaille
4
Muster 1° W O Cas
own observation
42
M 23
Messier
5
M 33
Messier
43
4 Sgr
Flamsteed
6
55 And
Flamsteed
44
5 Sgr
Flamsteed
7
M 34
own observation
45
M8
Le Gentil
8
M 45
–
46
M 69
Lacaille
9
M 38
Messier
47
M 20
Messier
10
M 42
Messier
48
7 Sgr
Flamsteed
M8
Messier
11
M1
Messier
49
12
M 36
Messier
50
M 21
Messier
13
M 37
Messier
51
M 24
Messier
14
M 35
Messier
52
M 16
Messier
15
M 41
Messier
53
M 18
Messier
16
M 50
own observation
54
M 17
Messier
17
M 81
own observation
55
J Sct
Hevelius
18
M 82
own observation
56
M 25
Messier
19
Cr 140
Lacaille
57
M 22
Lacaille
20
M 44
–
58
M 28
Messier
21
NGC 2477
Lacaille
59
M 26
Messier
22
NGC 2546
Lacaille
60
Q1 Sgr
Flamsteed
Messier
61
Q Sgr
Flamsteed
M 11
Messier Lacaille
23
M 40
2
24
M 40
Hevelius
62
25
M 51
own observation
63
M 55
26
M 53
own observation
64
V Cap
Hevelius
27
M 83
own observation
65
S Cap
Hevelius
28
[1 , [2, 17, 18 Lib
Hevelius
66
R Cap
Hevelius
29
M5
Messier
67
M 27
Messier
30
M 13
Messier
68
M 30
Messier
31
M4
Lacaille
69
M 29
Messier
32
M 12
own observation
70
M2
Messier
33
M 10
own observation
71
M 15
Messier
34
32, 33, 34 Oph
Hevelius
72
Z
Cyg
Hevelius
35
M 19
Messier
73
34, 35, 37 Peg
Hevelius
36
M9
Messier
74
?
Hevelius
37
M 14
Messier
75
M 39
Messier
38
88 Her
Hevelius
1+2
35
Three people had a significant influence on the extension of the Messier catalog: Camille Flammarion (1842–1925, French writer of popular astronomy), Helen Sawyer Hogg (1905–1993, professional Canadian astronomer), and Oswald Thomas (1882–1963, founder of the planetarium of Vienna).
ply confused M 89 with M 58. This yields the real identity of M 91 as NGC 4548.
M 102 The identity of this object has remained a matter of debate to the present day. Many modern US publications regard this object as “missing,” while most European sources identify it with the galaxy NGC 5866. This discussion has its origin in a letter, which Pierre Méchain wrote two years after the third version of the Messier catalog was completed, on the 6th of March 1783. He sent it to Bernoulli in Berlin, because Messier’s list of nebulae was also published in the Berlin Astronomical Almanac. Méchains letter was printed in the 1786 edition of the same almanac. In it, a passage reads: I would only like to add that Nr. 101 & 102 on p. 267 of the Connaissances des Temps for 1784 are nothing else than one and the same nebula, which was taken for two because of an error in the charts. In other words, Méchain said that M 102 was his accidentally repeated observation of M 101. Hartmut Frommert, however, came up with some serious doubts. Firstly, the descriptions of M 101 and M 102 given in the catalog differ from each other. And then, like M 103, M 102 had actually been observed and measured by Messier himself, as we know from his handwritten positions in his personal copy of the printed catalog. For M 103, there is an error of 1°, while there is no object near the position he noted for M 102. However, if he had made a simple mistake with the calculation, again by 5° as with M 48, but this time in right ascension, then there would be an object in the right place, which also
36
matches the description of M 102: NGC 5866. Hence, it is quite possible that Méchain accidentally observed M 101 twice, indeed, but that Messier then, while looking for the acclaimed object, found a real nebula – M 102 alias NGC 5866 was probably his last nebula discovery.
The supplementary Messier objects The original Messier catalog of 1784 contains 103 explicit entries. Nevertheless, today’s commonly accepted number of Messier objects is 110. The supplements have been added on in the twentieth century, according to evidence for objects observed by Messier but not (or not explicitly) included in his catalog. An important role is played by the above-mentioned letter of Méchain to Bernoulli, because it contains comments on further observed objects. The other important source is Messier’s personal copy of the catalog, which contains his handwritten notes. In 1924, Camille Flammarion discovered and bought that very copy, and he found Messier’s notes in it. One of them is about a further “very faint nebula in Virgo.” In his letter, Méchain wrote about this object and three others:
M 104 On 11th May 1781, I discovered a nebulous patch above Corvus which did not appear to me to contain single stars. It has a weak light and is difficult to find if the wires of the micrometer are illuminated. I compared it to Spica this day and the following and inferred the right ascension as 187° 9' 42", the southern
Discoverers of the Messier objects
Discoverers of the Messier objects
Discoverers of the Messier objects
Name
Discoverer
Messier’s Observation
Name
Discoverer
Messier’s Observation
Name
Discoverer
Messier’s Observation
M1
Bevis 1731
August 28th, 1758
M 37
Hodierna 1654
September 2nd, 1764
M 74
Méchain 1780
October 18th, 1780
M2
Maraldi 1746
September 11th, 1760
M 38
Hodierna 1654
M 75
Méchain 1780
October 5th, 1780
M3
Messier 1764
May 3rd, 1764
September 25th, 1764
M 76
Méchain 1780
October 21th, 1780
M 39
Messier 1764
October 24th, 1764
M 77
Méchain 1780
December 17th, 1780
M 40
Messier 1764
October 24th, 1764
M 78
Méchain 1780
December 17th, 1780
M 41
Hodierna 1654
January 16th, 1765
M 79
Méchain 1780
December 17th, 1780
M 80
Messier 1781
January 4th, 1781
M 81
Bode 1774
February 9th, 1781
M 82
Bode 1774
February 9th, 1781
M 83
Lacaille 1752
February 17th, 1781
M 84
Messier 1781
March 18th, 1781
M 85
Méchain 1781
March 18th, 1781
M 86
Messier 1781
March 18th, 1781
M 87
Messier 1781
March 18th, 1781
M 88
Messier 1781
March 18th, 1781
M 89
Messier 1781
March 18th, 1781
M 90
Messier 1781
March 18th, 1781
M 91
Messier 1781
March 18th, 1781
M 92
Bode 1777
March 18th, 1781
M 93
Messier 1781
March 20th, 1781
M 94
Méchain 1781
March 24th, 1781
M 95
Méchain 1781
March 24th, 1781
M 96
Méchain 1781
March 24th, 1781
M 97
Méchain 1781
March 24th, 1781
M 98
Méchain 1781
April 13th, 1781
M 99
Méchain 1781
April 13th, 1781
M 100
Méchain 1781
April 13th, 1781
M4 M5 M6 M7 M8 M9 M 10 M 11 M 12 M 13 M 14 M 15 M 16 M 17 M 18 M 19 M 20 M 21 M 22 M 23 M 24 M 25 M 26 M 27 M 28
de Chéseaux 1746 Kirch 1702 Hodierna 1654 Ptolemy 130 Flamsteed 1680 Messier 1764 Messier 1764 Kirch 1681 Messier 1764 Halley 1714 Messier 1764
th
May 8 , 1764 May 23rd, 1764 rd
May 23 , 1764
th
May 23rd, 1764
M 42
Peiresc 1611
March 4 , 1769
May 23rd, 1764
M 43
de Mairan 1744
March 4th, 1769
M 44
–
March 4th, 1769
May 29th, 1764
M 45
–
March 4th, 1769
May 30th, 1764
M 46
Messier 1771
February 19th, 1771
th
May 28 , 1764
th
May 30th, 1764
M 47
Hodierna 1654
February 19 , 1771
June 1st, 1764
M 48
Messier 1771
February 19th, 1771
M 49
Messier 1771
February 19th, 1771
st
June 1 , 1764
th
June 3rd, 1764
M 50
Cassini 1711
April 5 , 1772
de Chéseaux 1746
June 3rd, 1764
M 51
Messier 1773
October 13th, 1773
de Chéseaux 1746
rd
M 52
Messier 1774
September 7th, 1774
M 53
Bode 1775
February 26th, 1777
M 54
Messier 1778
July 24th, 1778 th
Maraldi 1746
June 3 , 1764
Messier 1764
June 3rd, 1764
Messier 1764
th
Messier 1764 Messier 1764 Ihle 1665 Messier 1764 Messier 1764
June 5 , 1764 June 5th, 1764
M 55
Lacaille 1752
July 24 , 1778
June 5th, 1764
M 56
Messier 1779
March 19th, 1779
M 57
Darquier 1779
January 31st, 1779
June 20th, 1764
M 58
Messier 1779
April 15th, 1779
June 20th, 1764
M 59
Köhler 1779
April 15th, 1779
th
June 5 , 1764
th
June 20th, 1764
M 60
Köhler 1779
April 15 , 1779
Messier 1764
June 20th, 1764
M 61
Oriani 1779
May 11th, 1779
Messier 1764
th
M 62
Messier 1771
June 7th, 1771
de Chéseaux 1746
Messier 1764
July 12 , 1764
th
July 27th, 1764
M 63
Méchain 1779
June 14 , 1779
Pigott 1779
March 1st, 1780
M 29
Messier 1764
July 29th, 1764
M 64
M 30
Messier 1764
August 3rd, 1764
M 65
Messier 1780
March 1st, 1780
M 66
Messier 1780
March 1st, 1780
M 67
Köhler 1779
April 6th, 1780
M 68
Messier 1780
April 9th, 1780
M 69
Lacaille 1752
August 31st, 1780
M 70
Messier 1780
August 31st, 1780
M 31 M 32
Al Sufi 964 Le Gentil 1749
rd
(1757) August 3 , 1764 (1757) August 3rd, 1764
M 33
Messier 1764
August 25th, 1764
M 34
Messier 1764
August 25th, 1764
M 71
de Chéseaux 1746
October 4 , 1780
M 35
de Chéseaux 1746
August 30th, 1764
M 72
Méchain 1780
October 4th, 1780
M 36
Hodierna 1654
September 2nd, 1764
M 73
Messier 1780
M 101
Méchain 1781
1781
M 102
Méchain 1781
1781
M 103
Méchain 1781
1781
M 104
Méchain 1781
May 11th, 1781
M 105
Méchain 1781
not observed
M 106
Méchain 1781
not observed
M 107
Méchain 1782
not observed
M 108
Méchain 1781
March 24th, 1781
M 109
Méchain 1781
March 24th, 1781
M 110
Messier 1773
August 10th, 1773
th
th
October 4 , 1780
37
declination 10° 24' 49". It is not tabulated in the Connoissance des Temps.
M 105 M. Messier thereat reports [in the catalog of 1774] p. 264 and 265, two nebulous stars, which I found in the Lion. I could not find fault with the noted positions, which were obtained by comparing them to Regulus. But there is a third a bit to the north, which is more vivid than the two preceding. I discovered it on March 24th, 1781, 4 or 5 days after I found the two others. On April 10th, I compared its position with J, obtaining a right ascension 159° 3' 45" and its southern declination 13° 43' 58".
M 106 In July 1781 I found another nebulous patch near the Great Bear next to the star No. 3 of the Hunting Dogs and 1° farther south, I estimated its right ascension 181° 40' and the northern declination approximately 49°. I will shortly try to determine the exact position of the same.
M 107 In April 1782 I discovered a small nebulous patch on the left shank of Ophiuchus between the stars ] and T, whose position I have not yet observed closely. In 1947 Helen Sawyer Hogg, who rediscovered the reprint of Méchains letter, suggested adding these four objects to the official Messier list in the order in which they are described. The printed catalog already mentioned M 108 and M 109 implicitly, in the note on M 97. These discoveries are also mentioned in the letter of Méchain, see below. This led Owen Gingerich to suggest, in 1953, adding them to the official Messier list, too.
38
M 108, M 109 Page 265 No. 97. A nebulous patch near E in the Great Bear. M. Messier remarks on two others, while noting its position, which I discovered as well and of which one is close to it, the other lies near J in the Great Bear, I have not been able to determine their positions yet. The last supplemental object (M 110), the second companion galaxy of M 31, was made an official Messier object by Kenneth Glyn Jones. As a matter of fact, Messier had already observed and sketched that dwarf galaxy in 1773. But for unknown reasons, he did not include it in his catalog, and his observing notes were published only in 1798, in the 1801 edition of the Connaissance des Temps. Did Messier and Méchain find any other objects? Apart from the above-cited hints given by Messier, there is also supporting evidence in Méchain’s letter to Bernoulli: On page 262 and 263 [of his last catalog version], M. Messier mentions several nebulous patches in the Virgin which I have indicated to him. But, there are more of them in the said area, which he did not see, and of which I will determine the positions, as soon as I have a convenient observing place, which will not be delayed too much. However, like Messier, Méchain did not continue with his nebula search. Apparently, he never found “a more convenient observing place,” and he was soon to become involved in other demanding work.
The catalog
Messier’s catalog exists in three versions: 1. First version from 1771, published in the Mémoires de l’Académie des Sciences, 1774 edition, objects 1 to 45. 2. Second version from 1780, published in the Connaissance des Temps, 1783 edition, objects 1 to 68. 3. Third version from 1781, published in the Connaissance des Temps, 1784 edition, objects 1 to 103. The following descriptions are a translation of the notes of the last version (from 1781). For each object, Messier also gives the date of his observation (which also is the equinox for the position), the right ascension in hours as well as in degrees, the declination in degrees, and (for most but not all objects) the angular diameter. Positive declinations are indicated by an “A,” negative by a “B.” For many objects discovered by Méchain, Messier lists both positional measurements, his and Méchain’s. The translation tries to maintain the character of the old-fashioned language, as well as Messier’s very individualistic use of a “:” for a “;.” Messier also indicates his other publications, referring to himself as “M.[onsieur] Messier.” The telescopes are characterized by their focal length.
The first catalog page of Messier’s third version from 1781 with the objects M 1 to M 5. For each object, the entries are the date of observation, object number, right ascension in h/min/s and deg/min/s, declination and diameter in degree/arcmin.
39
Table of the nebulae and, consequently, also the star clusters, which are found among the stars above the horizon of Paris, observed from the Observatory of the Navy. 1
Sep 12th 1758
5h 20min 2s
80° 0' 33"
Sep 11th 1760
21h 21min 8s
320° 17' 0"
1° 47' 0"A
0° 4'
Nebula without star in the head of the Water-Bearer, the center of it is brilliant, and the light which surrounds it is round; it resembles the fine Nebula which is found between the head and the bow of the Archer, it is very well seen in a refractor of two feet, placed on the parallel of a of the Water Bearer. M. Messier reported this nebula on the Chart of the path of the Comet observed in 1759, Mem. Acad. year 1760, page 464. M. Maraldi had seen this nebula in 1746, while observing the Comet that appeared in that year. 3
May 3rd 1764
13h 31min 25s
202° 51' 19" 29° 32' 57"B
0° 3'
Nebula discovered between the Herdsman & one of the Hunting Dogs of Hevelius; it does not contain any star, its center is brilliant & and its light fades insensibly, it is round; in a good sky one can see it with a refractor of one foot; it is reported on the Chart of the Comet observed in 1779. Memoirs of the Academy of the same year. Re-observed on March 29th 1781, always very beautiful. 4
May 8th 1764
16h 9min 8s
242° 16' 56" 25° 55' 40"A
0° 2½'
Cluster of very small stars; with a weak refractor it is seen in the form of a nebula; this star cluster is placed near Antares & at its parallel. Observed by M. de la Caille, & reported in his Catalogue. Re-observed on January 30th & March 22nd 1781. 5
May 23rd 1764
15h 6min 36s
226° 39' 4"
2° 57' 16"B
0° 3'
Fine Nebula discovered between the Scales & the Serpent, near the star of the Serpent, of the sixth magnitude, which is the fifth according to the Catalogue of Flamsteed: it does not contain any star; it is round, & one can see it very well, in a good sky, with a simple refractor of one foot. M. Messier reported it on the Chart of the Comet of 1763. Mem. Acad. year 1774, page 40. Re-observed on Sept. 5th 1780, January 30th & March 22nd 1781. 6
May 23rd 1764
17h 24min 42s 261° 10' 39"
32° 10' 34"A
0° 15'
Cluster of small stars between the bow of the Archer & the tail of the Scorpion. With the naked eye, this cluster seems to form a nebula; but with the smallest instrument which is employed to examine it, one sees a cluster of small stars.
40
May 23rd 1764
17h 38min 2s
264° 30' 24" 34° 40' 34"A
0° 30'
Cluster of more considerable stars than the previous; this cluster appears to the naked eye like a nebula, it is little away from the previous, placed between the bow of the Archer & the tail of the Scorpion.
21° 45' 17"B
Nebula below the southern horn of the Bull, does not contain any star; it is a whitish light, elongated in the shape of a candle’s light, discovered while observing the Comet of 1758. See the Chart of this Comet, Mem. Acad. year 1759, page 188; observed by Doctor Bevis about 1731. It is reported on the English star Atlas. 2
7
8
May 23rd 1764
17h 49min 58s 267° 29' 30" 24° 21' 10"A
0° 30'
Cluster of stars which appears in the form of a nebula when it is viewed with a simple refractor of three feet; but with an excellent instrument one does notice only a great number of small stars; near this cluster is a quite brilliant star, surrounded by a very faint light; this is the ninth star of the Archer, of the seventh magnitude, according to Flamsteed: this cluster appears in an elongated shape, which extends from North-east to South-west, between the bow of the Archer & the right foot of Ophiuchus. 9
May 28th 1764
17h 5min 22s
256° 20' 36" 18° 13' 26"A
0° 3'
Nebula, without star, in the right leg of Ophiuchus; it is round & its light faint. Re-observed on March 22nd 1781. 10
May 29th 1764
16h 44min 48s 251° 12' 6"
3° 42' 18"A
0° 4'
Nebula, without star, in the girdle of Ophiuchus, near the thirtieth star of that constellation, of sixth magnitude according to Flamsteed. This nebula is fine & round; one can see it only difficultly with a simple refractor of three feet. M. Messier reported it on the second Chart of the path of the Comet of 1769. Mem. Acad. year 1775, plate IX. Reobserved on March 6th 1781. 11
May 30th 1764
18h 30min 23s 279° 35' 43" 6° 31' 1"A
0° 4'
Cluster of a great number of small stars, near the star K of Antinous, that cannot be seen except in good instruments; with a simple refractor of three feet it resembles a Comet: this cluster is mingled with a faint light; in this cluster there is a star of 8th magnitude. M. Kirch observed it in 1681. Transact. Philos. No. 347, page 390. It is reported in the great English Atlas. 12
May 30th 1764
16h 34min 53s 248° 43' 10" 2° 30' 28"A
0° 3'
Nebula discovered in the Serpent, between the arm & the left side of Ophiuchus: this nebula does not contain any star, it is round & its light faint; near that nebula is a star of ninth magnitude. M. Messier reported it on the second Chart of the Comet observed in 1769. Mem. Acad. 1775, pl. IX. Re-observed on March 6th 1781. 13
Jun 1st 1764
16h 3min 15s
248° 18' 48" 36° 54' 44"B
0° 6'
Nebula without star, discovered in the girdle of Hercules; it is round & brilliant, the center brighter than the borders, one perceives it with a refractor of one foot; it is near two stars, both of 8th magnitude, one of them above & the other below: the nebula has been determined by comparing it with H of Hercules. M. Messier reported it on the Chart of the Comet of 1779, included in the Memoirs of the Academy, of the year 1784. Seen by Halley in 1714. Re-observed on Jan. 5th & 30th 1781. It is reported in the English star Atlas.
14
Jun 1st 1764
17h 25min 14s 261° 18' 29" 3° 5' 45"A
0° 7'
Nebula without star, discovered in the garment covering the right arm of Ophiuchus, & and placed on the parallel of of the Serpent; this nebula is not large, its light is faint, because of this it can be seen with an ordinary refractor of three & a half feet; it is round. Near it is a small star of the ninth magnitude; its position was determined by comparing it with of Ophiuchus, & M. Messier reported its position on the Chart of the Comet of 1769. Memoirs of the Academy, year 1775, plate IX. Re-observed on March 22nd 1781. 15
Jun 3rd 1764
21h 18min 41s
319° 40' 19" 10° 40' 3"B
0° 3'
Nebula without star, between the head of Pegasus & that of the small Horse; it is round, the center in it is brilliant, its position determined by comparing it with d of the small Horse. M. Maraldi, in the Memoirs of the Academy of 1746, speaks of this nebula: “I have seen, he said, between the star H of Pegasus & E of the small Horse, a star-nebula quite bright, that is composed of several stars; its right ascension is 319d 27' 6", & its southern declination is 11d 2' 22". 16
Jun 3rd 1764
18h 5min 0s
271° 15' 3"
13° 51' 44"A
Jun 3rd 1764
18h 7min 3s
271° 45' 48"
16° 14' 44"A
0° 5'
Train of light without stars, of five to six minutes in size, in the shape of a spindle, & a little bit like that in the girdle of Andromeda, but of a very faint light; there are two telescopic stars among & placed parallel to the Equator. In a good sky, one can see it very well with a simple refractor of three & a half feet. Re-observed March 22nd 1781. 18
Jun 3rd 1764
18h 6min 16s
271° 34' 3"
17° 13' 14"A
0° 5'
Cluster of small stars, a bit below the nebula above, No. 17, surrounded by a slight nebulosity, this cluster is less apparent than the previous, No. 16: with a simple refractor of three feet & a half, this cluster appears in the form of a nebula: but with a good refractor one only sees stars. 19
Jun 5th 1764
16h 48min 7s
252° 1' 45"
25° 54' 46"A
0° 3'
Nebula without stars, on the parallel of Antares, between the Scorpion & the right foot of Ophiuchus: this nebula is round; it is seen very well with a simple refractor of three & a half feet; the nearest known star to that nebula is the twenty-fifth of Ophiuchus, 6th magnitude, acc. Flamsteed. Re-observed on March 22nd 1781. 20
Jun 5th 1764
17h 48min 16s 267° 4' 5"
22° 59' 10"A
Cluster of stars, a little above the Ecliptic, between the bow of the Archer & the right foot of Ophiuchus. Re-observed on March 22nd 1781. 21
Jun 5th 1764
17h 50min 7s
22
Jun 5th 1764
18h 21min 55s
275° 28' 39" 24° 6' 11"A
0° 6'
Nebula, below the Ecliptic, between the head & the bow of the Archer, near a star of seventh magnitude, the twenty-fifth of the Archer, according to Flamsteed, this nebula is round, does not contain any star, & and can be seen very well with a simple refractor of three feet & a half; the star O of the Archer served for the determination. Abraham Ihle, German, discovered it in 1665, while observing Saturn. M. le Gentil observed it in 1747, & and he made an engraving of it, Memoirs of the Academy, year 1759, page 470. Re-observed on March 22nd 1781: it is reported in the English Atlas. 23
Jun 20th 1764
17h 42min 51s
265° 42' 50" 18° 45' 55"A
0° 15'
Cluster of stars, between the extremity of the bow of the Archer & the right foot of Ophiuchus, very near the star 65 of Ophiuchus, according to Flamsteed. The stars of the cluster are very near each other. Its position determined with P of the Archer.
0° 8'
Cluster of small stars, mingled with a faint light, near the tail of the Serpent, at small distance from the parallel of ] of that constellation; with a weak refractor it appears in the form of a nebula. 17
de according to Flamsteed. The stars of these two clusters are of the eighth to ninth magnitude, surrounded by nebulosity.
267° 31' 35" 22° 31' 25"A
Cluster of stars, near the previous; the nearest known neighboring star of these two clusters is the eleventh of the Archer, seventh magnitu-
24
Jun 20th 1764
18h 1min 44s
270° 26' 0"
18° 26' 0"A
1° 30'
Cluster of stars near the stars n & o of Antinous, among them is one of more light: with a telescope of three feet they cannot be distinguished, one has to employ a good instrument. This cluster does not contain any nebulosity. 25
Jun 20th 1764
18h 17min 40s 274° 25' 0"
19° 5' 0"A
0° 10'
Cluster of small stars in the neighborhood of the two previous clusters, between the head & the extremity of the bow of the Archer: the nearest known star to this cluster is the 21st star of the Archer, sixth magnitude, according to Flamsteed. The stars of this cluster are easily seen with a simple refractor of three feet; no nebulosity can be perceived. Its position was known by the star P of the Archer. 26
Jun 20th 1764
18h 32min 22s 278° 5' 25"
9° 38' 14"A
0° 2'
Cluster of stars near the stars n & o of Antinous, among them is one of more light: with a telescope of three feet they cannot be distinguished, one has to employ a good instrument. This cluster does not contain any nebulosity. 27
Jul 12th 1764
19h 49min 27s 297° 21' 41"
22° 4' 0"B
0° 4'
Nebula without star, discovered in the Fox, between the two forelegs, & very near the 14th star of this constellation, 5th magnitude according to Flamsteed; it is well seen with a simple refractor of 3 feet & a half: it appears in an oval shape, & does not contain any star. M. Messier reported its position on the Chart of the Comet of 1779, which will be engraved for the volume of the Acad. of the same year. Re-observed on January 31st 1781. 28
Jul 27th 1764
18h 9min 58s
272° 29' 30" 24° 57' 11"A
0° 2'
Nebula discovered in the upper part of the bow of the Archer about one degree from the star J & little distant from the fine nebula which
41
is between the head & arc. It does not contain any star; it is round, it cannot be observed without difficulty with a simple refractor of 3 feet ½. Its position was determined with J of the Archer. Re-observed on March twentieth 1781. 29
Jul 29th 1764
Aug 3rd 1764
21h 27min 5s
321° 46' 18" 24° 199' 4"A
0° 2'
Nebula discovered below the tail of the Capricorn, very near the 41 star of that constellation, 6th magnitude, according to Flamsteed. It can be seen with difficulty with a simple refractor of 3 feet ½. It is round & does not contain any star; its position determined by ] of the Capricorn. M. Messier reported it on the Chart of the Comet of 1759. Mem. Acad. 1760, pl. II.
36
Aug 3 1764
h
0 29
min
46
s
7° 26' 32"
39° 9' 32"B
0° 40'
The beautiful nebula in the girdle of Andromeda, in the shape of a spindle; M. Messier examined it with different instruments, & did not recognize any star: it resembles two cones or pyramids of light opposed by their base, the axis of which is in direction North-west to South-east; the two points of light or apexes are about 40 minutes of a degree apart; the common base of the two pyramids 15 minutes. This nebula was discovered in 1612, by Simon Marius, & observed since then by different astronomers. M. le Gentil gave a drawing of it in the Memoirs of the Academy of 1759, page 453. It is reported in the English Atlas. 32
Aug 3rd 1764
0h 29min 50s
7° 27' 32"
38° 45' 34"B
0° 2'
Small nebula without stars, below & by several minutes off that in the girdle of Andromeda; this small nebula is round, the light fainter than that of the girdle. M. le Gentil discovered it on October 29th 1749. M. Messier viewed it, for the first time, in 1757, & did not recognize any change. Aug 25th,1764
1h 40min 37s
20° 9' 17"
29° 32' 25"B
0° 15'
Nebula discovered between the head of the northern Fish & the great Triangle, at a small distance from a star of 6th magnitude: the nebula is of a whitish light, of almost equal density, however a little brighter for two thirds of its diameter, & does not contain any star. It can be seen difficultly with a simple refractor of one foot. Its position determined by comparing it with D of the Triangle. Re-observed on Sept. 27th 1780. 34
Aug 25th 1764
2h 27min 27s
36° 51' 37"
41° 39' 32"B
0° 15'
Cluster of small stars, between the head of the Medusa & the left foot of Andromeda, nearly on the parallel of J: with a simple refractor of 3 feet the stars can be distinguished. Its position was determined with E of the head of the Medusa.
42
24° 33' 30"B
0° 20'
Sep 2nd 1764
5h 20min 47s
80° 11' 42
34° 8' 6"B
0° 9'
Sep 2nd 1764
5h 37min 1s
84° 15' 12
32° 11' 51"B
0° 9'
Cluster of small stars, little distant from the previous, on the parallel of F of the Charioteer; the stars are very small, very close & contain nebulosity; with a simple refractor of 3 feet & a half, the stars are barely visible: this cluster is reported on the Chart of the second Comet of 1771, Mem. Acad. 1777. Sep 25th 1764
5h 12min 41s
78° 10' 12
36° 11' 51"B
0° 15'
Cluster of faint stars in the Charioteer, near the star V, at small distance from the two previous clusters; this one is of a square shape & does not contain any nebulosity, if examined with care in a good instrument. Its extent may be 15 minutes of a degree. 39
Oct 24th 1764
21h 23min 49s
320° 57' 10
47° 25' 0"B
1° 0'
Cluster of stars near the tail of the Swan; they can be seen with a simple refractor of 3 feet & a half. 40
Oct 24th 1764
12h 11min 2s
182° 45' 30
59° 23' 50"B
Two stars very near each other & very small, placed at the onset of the tail of the great Bear: they are barely distinguished with a simple refractor of 6 feet. These two stars have been observed while searching for the nebula placed above the back of the great Bear, reported in the book on the shape of celestial bodies, which must have been in 1660, 183d 32' 41" of right ascension, & 60d 20' 33" of north declination, which M. Messier could not see. 41
33
88° 40' 9"
Cluster of stars in the Charioteer, near the star I: with a simple refractor of 3 feet & a half the stars are barely discerned, the cluster does not contain any nebulosity. Its position determined with I.
38 31
5h 54min 41s
Cluster of very small stars, near the left foot of Castor, at little distance from the stars P & K of this constellation. M. Messier reported its position on the Chart of the Comet of 1770. Mem. Acad. 1771, pl. VII. Reported in the English Atlas.
37 st
rd
Aug 30th1764
20h 15min 38s 303° 54' 29" 37° 11' 57"B
Cluster of seven or eight very small stars, which are below J of the Swan, which are seen with a simple refractor of 3 feet & a half in the form of a nebula. Its position is determined with J of the Swan. This cluster is reported on the Chart of the Comet of 1779. 30
35
Jan 16th 1765
6h 35min 53s
98° 58' 12"
20° 33' 0"A
Cluster of stars below Sirius, near U of the great Dog; this cluster appears nebulous with a simple refractor of one foot: but it is only a cluster of small stars. 42
Mar 4th 1769
5h 23min 59s
80° 59' 40"
5° 34' 6"A
Position of the beautiful nebula of the sword of Orion, with the star T which is contained there with three other smaller stars which cannot be seen except in good instruments. M. Messier went into great detail on this great nebula; he has given a drawing of it, made with the most care, which can be seen in the Memoirs of the Academy, year 1771, plate VIII. It was Huyghens who discovered it in 1656: it was since then observed by a large number of astronomers. Reported in the English Atlas.
43
Mar 4, 1769
5h 24min 12s
81° 3' 0"
5° 26' 37"A
Position of the small star which is surrounded by nebulosity & which is below the nebula in the sword of Orion. M. Messier reported it on the drawing of the great one. 44
Mar 4, 1769
8h 7min 22s
126° 50' 30" 20° 31' 38"B
Cluster of stars known by the name of the nebulae of Cancer, the reported position is that of star C. 45
Mar 4, 1769
3h 33min 48s
53° 27' 4"
which appeared in the volume of the Academy on the same year 1779. Re-observed on April 10th 1781. 50
End of the printed catalog by M. Messier.
Those that follow have been observed by M. Messier, after the printing of his memoir. 7h 31min 11s
112° 47' 43"
14° 19' 7"A
Cluster of very small stars, between the head of the great Dog & the two hindlegs of the Unicorn, determined by comparing this cluster with the 2nd star of the Ship, 6th magnitude, according to Flamsteed; the stars are not visible except in a good refractor; this cluster contains a bit of nebulosity. 47
Feb 19th 1771
7h 44min 16s
116° 3' 58"
14° 50' 8"A
Cluster of stars little distant from the prev. the stars larger, the middle of the cluster compared with the same star, the second of the Ship. The cluster does not contain any nebulosity.
51
Feb 19th 1771
8h 2min 24s
120° 36' 0"
1° 16' 42"A
Cluster of very small stars, without nebulosity; this cluster is at a little distance from three stars which are at the onset of the tail of the Unicorn. Feb 19th 1771
12h 17min 48s 184° 26' 58" 9° 16' 9"B
Nebula discovered near the starG of the Virgin. It is not without difficulty that this nebula can be seen in a simple refractor of 3 feet & a half. The Comet of 1779 was compared to this nebula by M. Messier on April 22nd & 23rd: the Comet & the Nebula had the same brightness. M. Messier reported this nebula on the Chart of the path of this Comet,
13h 20min 23s 200° 5' 48"
48° 24' 24"B
Sep 7th 1774
23h 14min 38s 348° 39' 27" 60° 22' 12"B
Cluster of very small stars, mingled with nebulosity, which cannot be seen except in an achromatic refractor. While observing the Comet which appeared in that year, M. Messier saw this cluster, which had been near the Comet on September 7th 1774: it is below the star d of Cassiopeia: this star d served to determine the star cluster & the Comet. 53
Feb 26th 1777
13h 2min 2s
195° 30' 26" 19° 22' 44"B
Nebula without stars, discovered below & near the hair of Berenice, at a little distance from the 42nd star of this constellation, according to Flamsteed. This nebula is round & conspicuous. The Comet of 1779 was compared directly to this nebula, & M. Messier reported it on the Chart of this Comet, which will be included in the volume of the Academy for 1779. Re-observed on April 13th 1781: it resembles the nebula which is above the Hare. Jul 24th 1778
18h 40min 52s 280° 12' 55" 30° 44' 1"A
Very faint nebula, discovered in the Archer; its center is brilliant & does not contain any star, as seen with an achromatic refractor of 3 feet ½. Its position was determined with ] of the Archer 3rd magnitude. 55
49
Jan 11th 1774
Very faint nebula, without stars, near the ear of the southern of the Greyhounds, below the star K of 2nd magnitude of the tail of the Great Bear: M. Messier discovered this nebula on October 13th 1773, while observing the Comet which appeared in this year. One cannot see it but difficultly with a simple refractor of 3 feet ½: near it is a star of 8th magnitude. M. Messier reported its position on the Chart of the Comet observed in 1773 & 1774. Memoirs of the Academy 1774, plate III. It is double, each one with a brilliant center, separated from each other 4' 35". The two atmospheres touch each other. One is fainter than the other. Re-observed several times.
54 48
102° 57' 28" 7° 57' 42"A
Cluster of small stars more or less brilliant, below the right thigh of the Unicorn, above the star T of the ear of the great Dog, & near a star of 7th magnitude. M. Messier observed this cluster while observing the Comet of 1772. It is reported on the Chart of this Comet, on which it is traced. Mem. Acad. 1772.
52
Feb 19th 1771
6h 51min 50s
23° 22' 41"B
Cluster of stars, known by the name of the Pleiades. The reported position is that of the star Alcyone.
46
Apr 5th 1772
Jul 24th 1778
19h 26min 2s
291° 30' 25" 31° 26' 27"A
Nebula that is a whitish patch, about 6 minutes in extent, the light is even & appears not to contain any star. Its position was determined with ] of the Archer, by means of an intermediate star of 7th magnitude. This nebula was discovered by M. Abbé de la Caille. Mem. Acad. 1755, p. 194. M. Messier had searched for it without success on July 29th 1764, as reported in his Memoir.
43
56
Jan 23rd 1779
19h 8min 0s
287° 0' 1"
29° 48' 14"B
Nebula without star, having little light; M. Messier discovered it on the same day as the discovery of the Comet of 1779 on January nineteenth. On the 23rd, he determined its position by comparing it to the star No. 2 of the Swan, according to Flamsteed: it is near the milky way, near to it is a star of 10th magnitude. M. Messier reported it on the Chart of the Comet of 1779. 57
Jan 31st 1779
18h 45min 21s
281° 20' 8"
32° 46' 3"B
Mass of light placed between J & E of the Lyre, discovered while observing the Comet of 1779, which passed nearby: it seems that this mass of light, which is rounded, is composed of very small stars: with the best telescopes it is not possible to perceive them, there is only a suspicion left that they are there. M. Messier reported this mass of light on the Chart of the Comet of 1779. M. Darquier, in Toulouse, discovered this nebula, while observing the same Comet, & and he reports: “Nebula between J & E of the Lyre; it is quite lacklustre, but perfectly terminated; it is large as Jupiter & resembles a fading Planet.”
determined the position but approximately. Re-observed on March 22nd 1781. 63
58
Apr 15 1779
h
12 26
min
30
s
186° 37' 23" 13° 2' 42"B
Very faint nebula discovered in the Virgin, near the parallel of H 3rd magnitude. The least light to illuminate the micrometer wires causes it to disappear. M. Messier reported it on the Chart of the Comet of 1779, which can be found in the volume of the Academy of the same year. 59
Apr 15th 1779
12h 30min 47s 187° 41' 38" 12° 52' 36"B
Nebula in the Virgin & in the neighborhood of the previous, on the parallel of H, which served for the determination: it is of the same light as that above, just as faint. M. Messier reported it on the Chart of the Comet of 1779. 60
Sep 15th 1779
12h 32min 28s 188° 6' 53"
12° 46' 2"B
Nebula in the Virgin, a little bit more apparent than the two previous ones, likewise on the parallel of H, which has served for the determination. M. Messier reported it on the Chart of the Comet of 1779. He discovered these three nebulae while observing this Comet which passed very near to them. The latter passed very near on April 13th & 14th, that being both in the field of the refractor, he could not see it; it was not until the 15th, while searching for the Comet, that he saw this nebula. These three nebulae do not appear to contain any star. 61
May 11th 1779
12h 10min 44s
182° 41' 5"
5° 42' 5"B
Very faint nebula & difficult to perceive. M. Messier took this nebula for the Comet of 1779 on May 5th, 6th & 11th; on the 11th he recognized that this was not the Comet; but a nebula which was found on its path & at the same point in the Sky. 62
June 4th 1779
16h 47min 14s 251° 48' 24" 29° 45' 30"A
Very fine nebula, discovered in the Scorpion, it resembles a small Comet, its center is brilliant & surrounded by a faint light. Its position was determined by comparing it to the star W of the Scorpion. M. Messier had already seen this nebula on June 7th 1771, without having
44
13h 4min 22s
196° 5' 30"
43° 12' 37"B
Nebula discovered by M. Méchain in the Hunting Dogs. M. Messier located it; it is faint, it has about the same brightness as the nebula reported under No. 59: it does not contain any star, & the least light to illuminate the wires of the micrometer causes it to disappear: there is a star of 8th magnitude near it, which precedes the nebula on the hour wire. M. Messier reported its position on the Chart of the path of the Comet of 1779. 64
Mar 1st 1780
12h 45min 51s
191° 27' 38" 22° 52' 31"B
Nebula discovered in the hair of Berenice, which is half as apparent as that one which is below the hair. M. Messier reported its position on the Chart of the Comet of 1779. Re-observed on March seventeenth 1781. 65
th
June 14th 1779
Mar 1st 1780
11h 7min 24s
166° 50' 54" 14° 16' 8"B
Nebula discovered in the Lion; it is very faint & does not contain any star. 66
Mar 1st 1780
11h 8min 47s
167° 11' 39"
14° 12' 21"B
Nebula discovered in the Lion; its light very faint & very near the previous: they appear both in the same field of the refractor. The Comet observed in 1773 & 1774 had passed between these two nebulae from November 1st to 2nd 1773. M. Messier did not see them then, without doubt, because of the light of the Comet. 67
Apr 6th 1780
8h 36min 28s
129° 6' 57"
12° 36' 38"B
Cluster of small stars with nebulosity, below the southern Claw of the Crab. The position determined with the star D. 68
Apr 9th 1780
12h 27min 38s 186° 54' 33" 25° 30' 20"A
Nebula without stars below the Raven & the Hydra; it is very faint, very difficult to perceive with the refractors; near it is a star of the sixth magnitude.
Extension of the Catalog of Nebulae & Star Clusters of M. Messier, included in the Connoiss. des Temps for 1783, page 225, & year 1784, page 255 & following. 69
Aug 31st 1780
18h 16min 47s
274° 11' 46"
32° 31' 45"A
0° 2'
Nebula without stars, in the Archer, below his left arm & near the arc; near it is a star of 9th magnitude: its light is very faint, one cannot see it but in good weather, & the least light employed to illuminate the wires of the micrometer causes it to disappear: its position was determined by H of the Archer: this nebula was observed by M. de la Caille, & reported in his catalog; it resembles the nucleus of a small Comet. 70
Aug. 31st 1780
18h 28min 53s
277° 13' 16"
32° 31' 7"A
0° 2'
Nebula without star, near the previous, & on the same parallel: near it is a star of the ninth magnitude & four small telescopic stars, nearly on a straight line, very near each other, & are placed above the nebula, as seen in an inverting refractor; the nebula determined by the same star H of the Archer. 71
Oct 4th 1780
19h 43min 57s
M. Méchain
295° 59' 9"
18° 13' 0"B
296° 0' 4"
18° 14' 21"
0° 3 ½'
Nebula discovered by M. Méchain on June 28th 1780, between the stars J & G of the Arrow. On the following October 4th, M. Messier located it: its light is very faint & does not contain any star; the least light causes it to disappear. It is placed about 4 degrees below that which was discovered by M. Messier in the Fox. See No. 27. He reported it on the Chart of the Comet of 1779. 72
Oct 4th 1780
20h 41min 23s
M. Méchain
310° 20' 49"
13° 20' 51"A
310° 21' 10"
13° 21' 24" th
Oct 4th & 5th 1780 20h 46min 52s
311° 43' 4"
Oct 18th 1780 M. Méchain
1h 24min 57s
M. Méchain
76
13° 28' 40"A
21° 14' 9"
14° 39' 35"B 14° 36' 0"
Oct 21st 1780
1h 28min 43s
M. Méchain
298° 17' 24"
22° 32' 23"A
298° 17' 30"
22° 32' 0"
22° 10' 47"
50° 28' 48"B
22° 10' 26"
50° 28' 12"
0° 2'
Nebula on the foot of Andromeda, seen by M. Méchain on Sept. 5th 1780, & of which he reports: “This nebula does not contain stars; it is small & faint.” On the following October 21st M. Messier located it with his achromatic refractor, & it seemed to him that it was composed of nothing but very small stars, which contained nebulosity, & the least light employed to illuminate the wires of the micrometer caused them to disappear: the position determined with the star I of Andromeda, fourth magnitude. 77
Dec 17th 1780
2h 31min 30s
M. Méchain
37° 52' 33"
0° 57' 43"A
37° 52' 58"
0° 57' 44"
Cluster of small stars, which contain nebulosity, in the Whale, & on the parallel of the star G reportedly of third magnitude, & which M. Messier estimated to be only of the fifth. M. Méchain saw this cluster on October 29th 1780 in the form of a nebula. 78
21° 17' 0"
19h 53min 10s
Nebula without star, between the Archer & the head of the Capricorn: seen by M. Méchain on August 27th & 28th 1780. M. Messier located it on October 5th following & on the eighteenth compared it with the star No. 4, sixth magnitude of the Capricorn, according to Flamsteed: it appears to M. Messier that it is composed only of very small stars, containing nebulosity: M. Méchain reported it as nebula without stars. M. Messier saw it on October 5th; but the Moon was on the horizon, & it was not until the eighteenth of the same month that he was able to judge its appearance & determine its position.
th
Cluster of three or four small stars, which resemble a nebula at first glance, contains a bit of nebulosity: this cluster is placed on the parallel of the previous nebula: its position was determined by the same star Q of the Water-Bearer. 74
Oct 18th 1780
0° 2'
Nebula seen by M. Méchain the night of August 29 to 30 1780, above the neck of the Capricorn. M. Messier located it on October 4th & 5th following: its light faint as the previous; near it is a small telescopic star: its position determined with the star Q of the Water-Bearer, fifth magnitude. 73
75
Nebula without star, near the star K of the Link of the Fishes, seen by M. Méchain at the end of September 1780, & and of which he reports: “This nebula does not contain stars; it is quite large, very obscure, extremely difficult to observe, one can determine it more exactly in good frosts.” M. Messier located it & found it, as M. Méchain described it: it was compared directly with the star K of the Fishes.
Dec 17th 1780
5h 35min 34s
M. Méchain
83° 53' 35"
0° 1' 23"A
83° 53' 2"
0° 0' 31"
0° 3'
Cluster of stars, with much nebulosity in Orion & on the parallel of the star G of the Belt, which served in determining its position; the cluster follows the star on the hour wire by 3d 41' & the cluster above the star by 27' 7". M. Méchain has seen this cluster in the beginning of 1780, & reports hence: “On the left side of Orion, 2 to 3 minutes of diameter, there are two fairly brilliant nuclei, surrounded by nebulosity.” 79
Dec 17th 1780
5h 15min 16s
M. Méchain
78° 49' 2"
24° 42' 57"A
78° 47' 10"
24° 44' 46"
Nebula without star, placed below the Hare, & on the parallel of a star of the sixth magnitude: seen by M. Méchain on October 26th 1780. M. Messier located it on December seventeenth following: this nebula is fine; the center brilliant, the nebulosity little diffuse: its position determined by the star H of the Hare, fourth magnitude. 80
Jan 4th 1781 M. Méchain
16h 4min 0s
240° 59' 48"
22° 25' 13"A
241° 0' 26"
22° 27' 58"
0° 2'
Nebula without star, in the Scorpion, between the stars J & G, compared with J to determine its position: this nebula is round, the center brilliant & resembles the nucleus of a small Comet, surrounded by nebulosity. M. Méchain saw it on January 27th 1781.
45
81
Feb 9th 1781
9h 37min 51s
M. Méchain
144° 27' 44" 70° 7' 24"B 144° 27' 0" 70° 4' 0"
Nebula near the ear of the great Bear, on the parallel of the star d, of the fourth to the fifth magnitude: its position determined with this star. This nebula is slightly oval, the center clear, & it can be seen very well with a simple refractor of three feet & a half. It was discovered at Berlin, by M. Bode, on December 31st 1774, & by M. Méchain, in the month August of 1779.
nebula in the field of the refractor. Its light is one of the faintest & resembles that reported in the Virgin, No. 58. 89
82
Feb 9 1781
h
9 37
min
57
s
M. Méchain
144° 29' 22" 70° 44' 27"B 144° 28' 13" 70° 43' 5"
Nebula without star, near the previous; both appear in the field of the refractor at the same time, this one less apparent than the previous, its light is faint & elongated: at its extremity is a telescopic star. Seen at Berlin, by M. Bode, on December 31st 1774, & by M. Méchain, in the month August of 1779. 83
Feb 17th 1781
13h 24min 33s 201° 8' 13"
28° 42' 27"A
Nebula without star, near the head of the Centaur: it appears as a faint & even light, but so difficult to observe, that the least light to illuminate the wires of the micrometer causes it to disappear. It is only with much attention that it can be seen: it forms a triangle with two stars estimated of the sixth and seventh magnitude: determined with the stars l, i, k, h, of the head of the Centaur: M. de la Caille had already determined this nebula. See at the end of this Catalog. 84
Mar 18th 1781
12h 14min 1s
183° 30' 21" 14° 7' 1"B
Nebula without star, in the Virgin; its center is rather bright, surrounded by a light nebulosity: its brightness & its appearance resemble those of this Catalog, Nos. 59 & 60. 85
Mar 18th 1781
12h 14min 21s
M. Méchain
183° 35' 21" 19° 24' 26"B
12h 15min 5s
91
Mar 18th 1781
12h 19min 48s 184° 57' 6"
13° 38' 1"B
Nebula without star, in the Virgin, below & quite near of a star of eighth magnitude, the star having the same right ascension as the nebula, & its declination is 13d 42' 21" north. This nebula appears of the same brightness as the two nebulae Nos. 84 & 86. 88
Mar 18th 1781
12h 21min 3s
185° 15' 49" 15° 37' 51"B
Nebula without star, in the Virgin, between two small stars & and one star of the sixth magnitude, which appear at the same time as the
46
12h 25min 48s 186° 27' 0"
14° 22' 50"B
Mar 18th 1781
12h 26min 28s 186° 37' 0"
14° 57' 6"B
Nebula without star, in the Virgin, above the previous No. 90: its light is still fainter than those above. Note. The constellation of the Virgin, & especially its northern wing, is one of the constellations which encloses many Nebulae: this Catalogue contains 13 of them determined: namely, the Nos. 49, 58, 59, 60, 61, 84, 85, 86, 87, 88, 89, 90 & 91. All these nebulae appear without stars: they cannot be seen except in a very good sky, & near their passages of the Meridian. The majority of these nebulae were indicated to me by M. Méchain. 92
Mar 18th 1781
17h 10min 32s
257° 38' 3"
43° 21' 59"B
0° 5'
Nebula, fine, conspicuous, & of a great brightness, between the knee & the left leg of Hercules, seen very well with a refractor of one foot. It does not contain any star; the center is clear & brilliant, surrounded by nebulosity & resembles the nucleus of a big Comet: its light, its magnitude, come very near to that of the nebula which is in the girdle of Hercules. See No. 13 of this Catalog: its position was determined by comparing it directly to the star R of Hercules, fourth magnitude: the nebula & star on the same parallel. 93
Mar 20th 1781
7h 35min 14s
113° 48' 35"
23° 19' 45"A
0° 8'
Cluster of small stars, without nebulosity, between the great Dog & the prow of the Ship.
183° 46' 21" 14° 9' 52"B
Nebula without star, in the Virgin, on the parallel & very near of the nebula above, No. 84: their appearance is the same, & both appear the same field of the refractor. 87
Mar 18th 1781
Nebula without star, in the Virgin: its light as faint as the previous, No. 89.
94 Mar 18th 1781
13° 46' 49"B
183° 35' 45" 19° 23' 0"
Nebula without star, above & near the spike of the Virgin, between the two stars of the hair of Berenice, Nos. 11 & 14 of Flamsteed’s Catalog: this nebula is very faint. M. Méchain determined its position on March 4th 1781. 86
12h 24min 38s 186° 9' 36"
Nebula without star, in the Virgin, at a little distance from & on the same parallel as the nebula reported above, No. 87. Its light was extremely faint & rare & it is not without trouble that it can be perceived. 90
th
Mar 18th 1781
Mar 24th 1781
12h 40min 43s 190° 10' 46" 42° 18' 43"B
M. Méchain
0° 2 ½'
190° 9' 38" 42° 18' 50"
Nebula without star, above the heart of Charles, on the parallel of the star No. 8, sixth magnitude, of the Greyhounds, according to Flamsteed: its center is brilliant & the nebulosity slightly diffuse. It resembles the nebula which is below the Hare, No. 79: but this one is finer & more brilliant; M. Méchain did discover it on March 22nd 1781. 95
Mar 24th 1781 M. Méchain
10h 32min 12s
158° 3' 5"
12° 50' 21"B
158° 6' 23"
12° 49' 50"
Nebula without star, in the Lion, above the star l: its light is very faint.
96
Mar 24th 1781
10h 35min 5s
M. Méchain
By M. Méchain, which M. Messier has not yet seen.
158° 46' 20" 12° 58' 9"B 158° 48' 0" 12° 57' 33"
Nebula without star, in the Lion, near the previous; this one is less apparent, both on the parallel of Regulus: they resemble the two nebulae in the Virgin, Nos. 84 & 86. M. Méchain saw both on March twentieth 1781. 97
Mar 24th 1781
11h 1min 15s
165° 18' 40" 56° 13' 30"A
0° 2'
Nebula in the great Bear, near E: it is difficult to observe, reports M. Méchain, especially when illuminating the wires of the micrometer: its light is faint, without star. M. Méchain saw it for the first time on February 16th 1781, & the position is given according to him. Near this nebula he has seen another, which has not been determined yet, also a third one which is near to J of the great Bear. 98
Apr 13th 1781
12h 3min 23s
101 Mar 27th 1781
13h 43min 28s 208° 52' 4"
55° 24' 25"B
0° 7'
Nebula without star, very obscure & pretty large, 6 to 7 minutes in diameter, between the left hand of the Herdsman & the tail of the great Bear. It can be barely distinguished when the wires are lit. 102
Nebula between the stars R of the Herdsman & L of the Dragon: it is very faint; near it is a star of the sixth magnitude. 103
Cluster of stars between H and G of the leg of Cassiopeia.
180° 50' 49" 16° 8' 15"B
Nebula without star, of an extremely faint light, above the northern side of the Virgin, on the parallel & near the star No. 6, fifth magnitude, according to Flamsteed. M. Méchain saw it on March 15th 1781. 99
Apr 13th 1781
12h 7min 41s
181° 55' 19" 15° 37' 12"B
Nebula without star, of a very rare light, but a little bit more clear than the previous, placed on the northern side of the Virgin, & near the same star, No. 6, of the hair of Berenice. The nebula is between two stars of the seventh & eighth magnitude. M. Méchain observed it on March 15th 1781. 100 Apr 13th 1781
12h 11min 57s
182° 59' 19" 16° 59' 21"B
Nebula without star, of the same brightness as the previous, placed in the spike of the Virgin. Seen by M. Méchain on March 15th 1781. These three nebulae, Nos. 98, 99 & 100, are very difficult to distinguish, because of the faintness of their light: they cannot be seen except in good weather, & near their passages of the Meridian.
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Remarks on Messier’s catalog Messier’s catalog is, by no means, a uniform series of observations. The descriptions stem from the use of different telescopes (see box) and are, consequently, of varying quality. The object brightness, which Messier would still see or describe as faint, varies accordingly. The faintest object of the first catalog version is also its first, M 1 with magnitude 8.4. Almost all other entries are brighter than 8th magnitude, most fall even into the range of 5th to 7th magnitude. Apart from M 31, M 32, and M 33, no galaxies are listed in the first catalog version; they were too faint for Messier’s instrumentation at that time. Hence, most of the first 45 entries are open clusters, some globular clusters and a few galactic nebulae, plus one single planetary nebula. For his second catalog, Messier was able to use better optical instruments. By 1773 he had received one of the first achromatic refractors from the collection of his friend de Saron. This telescope is mentioned in detail in the description of Messier’s drawing of M 42. From then on, Messier’s discoveries reach nearly down to magnitude 10, including many galaxies. This trend continues with the third part, which includes objects at the perception limit of a modern 2-inch telescope under a dark sky. Many of these were contributed by Méchain, who worked at the Royal Observatory – we may safely assume that his instruments were better than Messier’s. Messier’s first catalog (M 1 to M 45) contains exact descriptions of the telescopes and magnifications he used. The telescope mentioned in almost every more detailed description is a Gregorian reflector of 30 inches (French) focal length, 6 inches aperture and a (probably fixed) magnification of 104×. Modern notation would have it as a 6.4-inch f/5 system (162mm aperture, 810mm focal length) with an eyepiece focal length of 7.8mm. With an apparent field of view of 30°, it covered 17' in the sky. This telescope is mentioned in the descriptions of M 2, 3, 5, 9, 10, 11, 15, 19, 22, 26, 27, 28, 30, 31, 35, 42, and 43, while for M 13 and M 31, a Newtonian telescope of 4.5-feet focal length and a power of 65× is noted. It is most likely that Messier made his discoveries with smaller telescopes, which he used for comet hunting. The purpose of the larger optics was to make detailed descriptions and to measure the positions of the new objects. In the third catalog, Messier ranks his telescopes according to their focal length in five categories. These were also used by him to characterize the difficulty of an object:
A page from Messier’s observing logbook. In his entry made on the 7th of July 1758, Messier describes the reflector with which he observed the moons of Jupiter and stellar occultations. As shown here, the telescope is set up for measurements of the exact eyepiece focal length.
1 foot observed objects: M 3, M 5, M 13, M 33, M 41, M 92
2 foot The faintest of these targets is M 92 at magnitude 6.4. M 41 was not recognized by Messier as a star cluster but taken for a nebula. Since its brightest stars reach magnitude 6.9, the limiting magnitude of this telescope under the Parisian night sky must have been between magnitudes 6.5 and 7.0.
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observed objects: M 2 The optical performance of this telescope cannot have been much better than that of the 1-foot telescope.
3 foot observed objects: M 8, M 10, M 11, M 25, M 26, M 30, M 34, M 35 The faintest of these objects is M 26 with magnitude 8.0. However, M 10 at magnitude 6.6 was already characterized as “difficult” by Messier, and resolving the stars of M 25 beginning at magnitude 6.7 was not easy for him, either. He barely resolved M 34 (brightest stars magnitude 7.3), but not M 11 (brightest stars magnitude 8) which he described as a nebula when seen with this instrument, likewise with M 35, which Messier could resolve only with the Gregorian telescope. Hence, the limiting magnitude of the 3-foot refractor must have been between magnitudes 7.5 and 8.0.
3.5 foot observed objects: M 14, M 17, M 18, M 19, M 22, M 23, M 26, M 27, M 28, M 29, M 30, M 32, M 36, M 37, M 39, M 49, M 51, M 81 The faintest of these objects is the Virgo cluster galaxy M 49 at magnitude 8.4. Like M 28, M 30, and M 51, it appeared “very faint” to Messier. Some star clusters remained unresolved: M 18 (brightest stars magnitude 8.7), M 29 (brightest stars 8.6), M 36 (brightest stars 8.7), and M 37 (brightest stars 9.2). This indicates a limiting magnitude of 8.5.
6 foot The only time Messier mentions this focal length is in connection with M 40. He described this stellar pair of magnitudes 9.0 and 9.3 as nebulous, and we may infer a limiting magnitude of around 10.0 from that. For the remaining objects, Messier did not specify which telescopes were used. These include many of the entries in the third version of the catalog. However, it is likely that Messier chiefly employed the 3.5-inch f/12 achromatic refractor (89mm aperture, 1067mm focal length), which he had received from de Saron and described as his favorite instrument. This telescope was mentioned without full details several times, for example in the descriptions for M 54 (observed 1778) and M 76. One criterion Messier used to describe an object as faint was its inability to be seen even when the micrometer’s illumination was set at its lowest level. In this category we find M 58, 59, 63, 69, 71, 76, 83, 88, 89, 90, 91, 97, 98, 99, and M 100, all observed after 1779. The faintest of these are M 76, M 98, and M 91 at magnitude 10.1. Messier could resolve the brightest stars in the clusters M 4 (magnitude 10.8), M 46 (brightest stars 8.7), M 52 (brightest stars 8.2), and M 67 (brightest stars 9.7). But M 71 (brightest stars magnitude 12.1) and other globular clusters remained a “nebula without stars.” Hence, the telescopic limiting magnitude must have been about 11.0 for the 6.4-inch Gregorian he used in the first edition, as well as for the 3.5-inch Dollond he prefered later. Modern visual observers are puzzled by the lack of observed detail reported by Messier. The only globular cluster in which he was able to see the brightest stars was M 4 – the rest remained a “nebula without stars” to him. By contrast, a modern 3.5-inch refractor under dark skies would resolve the brightest stars in at least half a dozen of Messier’s globular clusters. Furthermore, it appears that Messier had not seen any of the true nebulosity of M 20, and he probably mistook M 76 and M 78 for star clusters. He even believed that he saw stars in M 57, which had been described correctly as a nebulous disk by its discoverer Darquier already. Méchain, in particular, seems to have carried out better observations than Messier in that respect. Good examples are their different descriptions of the four objects M 75 to M 78, in which Messier disagrees with Méchain’s notes:
Why were some showpieces left out by Messier? The Messier catalog includes most of the finest showpieces in the night sky, but a few were left out. Since these missing objects were easily within reach of Messier’s telescopes, many deep-sky observers have been puzzled about their omission. The reason is simple: Messier was not interested in deep-sky objects for their own sake. Instead, he did not want to confuse them with comets. He did not look for them in a systematic way, not even during those few months of intensive searching. That separates him from William Herschel, who started to work on his impressive catalog in 1782. But considering the often accidental findings of Messier, his catalog is rather surprisingly complete. The puzzling question in this context is: why then did Messier add four well-known spectacular objects, M 42 to M 45, to his initial list of 41? Certainly, these were not to be confused with a comet. Probably, in this one instance, Messier was tempted to round up his list to a number larger than the 42 objects of his role-model Lacaille. But at the same time, there were not enough showpieces to make it to the next round number, 50 – so he left some out. The most prominent example is the double cluster h & Fin Messier’s days known as F Per. Messier must have known it, and his contemporary Bode described its field as “to the north of the star F a lot of small stars, looks nice in telescopes.” The fact that this object already had a proper designation and was shown by all star-charts may have been the very reason why Messier did not include it in his list. Several other bright objects were just too large for the field of view of Messier’s telescopes. Good examples are the widely spread star clusters IC 4665 or the “coat-hanger,” Collinder 399, which would not have been obvious through Messier’s eyepiece. Messier also knew of some objects in the southern sky, but he wanted a catalog of objects that are all observable from Paris, and which he had observed in person. And it is this last of his principles that made his catalog stand out in quality from the lists of his contemporaries. The resulting low number of errors in Messier’s list also made his catalog successful.
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Messier’s telescopes Which telescopes did Messier use to discover and to observe his 110 objects? The answer is not easy to give, for three reasons: firstly, hardly any sources have survived which would describe the contemporary instrumentation of the observatory at the Hôtel de Cluny. Secondly, Messier used a variety of telescopes of five different categories, as we know from his descriptions. And thirdly, with the gradual availability of achromatic lenses, there was a tremendous change in optical telescope quality around the time the catalog was accomplished. In the seventeenth century, telescopes with chromatic lenses (i.e., refractors without colorcorrection) were the standard. They had a single objective lens and an eyepiece made of two lenses. The construction principles had been optimized by Christian Huygens. In order to keep the chromatic aberration of the objective lens within limits, these refractors had to have extremely long focal lengths: an aperture of 70mm required a length of 8m! Therefore, the telescopes were made of two movable parts, both riding on a long rod. With the longest telescopes, they were connected only by a rope under tension. The objective lens was at the far upper end, mounted on a high pole or stepladder by means of a simple ball-head. The eyepiece at the lower end by the observer resided on a small stepladder. Equatorial mounts were not yet known, and a tube would have been too heavy for these long telescopes. The long focal lengths imposed magnifications of over 100× and very small fields of view. In our time, it is hard to imagine how cumbersome any telescopic observation must have been in those days. First, the object had to be carefully aimed at with the rod. Then, with a most gentle touch, the remote ball-head, supporting the objective lens at the far end, had to be fixed. Tracking the object with this clumsy construction and a magnification of over 100× must have required a lot of training and patience. Despite such disadvantages, all major astronomical discoveries between 1650 and 1730 had been achieved with this kind of chromatic refractor, and even whole maps of the moon had been drawn!
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We can be pretty certain that Messier’s “ordinary refractors” of 1, 2, 3, 3.5, and 6-foot focal length were exactly that kind of clumsy, chromatic telescope. He favored the smaller telescopes with focal lengths of 1 meter or less, because these had a tube which reduced stray light and greatly facilitated their use. But even Messier’s 6-foot refractor was a dwarf compared to the longest contemporary refractors with focal lengths of over 30m. Around the mid-eighteenth century, coinciding with Messier’s active period, the time of these monstrous telescopes finally came to an end as the result of two new developments: first, James Short (1710–1768), a London-based optiContemporary impression of a tubeless chromatic cian, developed a method to produrefractor in the seventeenth century. The objective ce telescope primary mirrors from (i) is mounted and counterbalanced (k–l) on a shiny metal-alloys (front-silvered ball-head (m). It is connected with the eyepiece glass-mirrors would come only la(o) by a rope under tension. This cumbersome ter). From 1743 to 1768, Short was construction was dictated by the long focal length the first to produce telescopes in of the single objective lens, required to keep the large numbers. 1400 Short-reflecchromatic aberration as small as possible. tors were made by his little company, mostly employing the Gregorian design and mounted on a short table-top stand or ordinary tripod. many years before he could lay his hand on For quite some time, Short’s reflectors were one of these fine telescopes – which was not regarded as the best telescopes worldwide. His until his rich friend de Saron gave him one. largest mirrors would reach 22 inches diameIn 1772, Dollond’s patent rights expired, and ter! in the face of new competition, the prices for The second important invention was made his telescopes dropped considerably. Still, for only a little later, also in London: the achromany years Dollond’s company remained the matic (color-corrected) refractor. The idea of most important producer of achromatic recombining lenses from two different types of fractors – a technical term, by the way, which glass to minimize the color aberration already was coined by John Bevis, the discoverer of existed, but it was the optician John Dollond M 1. (1706–1761), who secured the patent rights In the 1807 edition of the Connaissance des and started large-scale production of achroTemps, Messier published a list of telescopes matic refractors in 1758. After his death, his he had used in the years 1765 to 1769, in son took over and expanded the company. his work on the first catalog of 45 objects. In the beginning, Dollond’s refractors were However, their specifications almost excluvery expensive, due to extraordinary desively refer to the focal lengths, given in the mand. Hence, working in an observatory with French foot (slightly larger than the respechumble financial means, Messier had to wait tive English units: 1 French foot = 0.3248 m
= 12 French inch, 1 French inch = 2.7cm), rarely to the aperture. However, from that source, and from a few more remarks in the literature, we know at least some of the telescopes available to Messier: 1) Chromatic refractors of short focal length (“lunettes ordinaires” or “ordinary refractors”) and, possibly, draw-tube telescopes with erect images. The focal lengths were between 1 foot and 3.5 feet, none of the apertures were more than 3.5 inches (80mm), and their optical performance scarcely reached that of modern Dollond refractors, the first achromatic refractors binoculars. produced in large numbers, arrived on the optical 2) Chromatic refractors of market in 1758. Messier used such a telescope long focal length (25 to 30 with 90mm (3.5 inches) of aperture for many of feet or 8.1m to 9.7m), with his deep-sky observations. magnifications of 102× to 138×. These were built according to the principles developed by Huygens, with an f-ratio of over century optics had no coating and, because of 1:100 to keep color aberration under control. their inferior transmission, had a smaller efHence, the respective telescopes at hand for fective aperture by today’s standards. In 1771, Messier would have been between 70/8100 Messier used a low-power (27×) 3.5-feet mm and 80/9740 mm. It was already pointed achromatic refractor for comet observation, out how cumbersome their use was in nightalso given to him by his friend de Saron. For ly practice, providing only a very small field his stay in Lorraine in 1772, he took another of view, and this is why Messier as a comet achromatic refractor from de Saron with him. hunter hardly ever used them. In addition, a It had a focal length of 5 feet, magnified 60×, Campani refractor is mentioned, with a maand was made by the optician Lestang. He gnification of 64× and coming from a sevenalso took an “ordinary [chromatic] refractor” teenth-century optical workshop. It, too, had of 3.5 feet and a possibly achromatic refractor a chromatic lens with very long focal length. of 2 feet (“lunette de nuit”). In the publica3) Achromatic Dollond-refractor with 3¼ tion of a solar observation in 1777, Messier French-foot (1.07 m) focal length and a mareported use of a 3.5-feet achromat with a gnification of 120×. This telescope appears to triplet-lens objective. And in 1781, he mentibe the one which Messier had described as his oned a small achromatic refractor of 405mm favorite instrument, given to him by de Saron. focal length, as well as a “large achromatic It was specified (in English measurements) as refractor on an equatorial machine” – equahaving a 42-inch focal length and 3.5-inch torial mounts would become more common aperture (89/1067mm) and had the same observatory equipment only in the nineteenth magnification of 120×. It is mentioned in the century, after Joseph Fraunhofer invented descriptions of M 54 and M 76. We have to what is known today as the German equatoconsider, however, that the late-eighteenthrial.
Gregorian reflectors made by Short were in widespread use at the end of the eighteenth century. Apart from a large telescope with a 310mm aperture, Messier used a smaller model similar to the one pictured here.
4) Gregorian reflector made by Short with 6-feet (1.95m) focal length and a magnification of 110×. The optical specifications of Short’s telescopes are known very well from his price lists. A telescope of such a focal length had the remarkable aperture of 12 inches. In addition, Messier mentioned a Short reflector of only 1 foot focal length with 44× magnification, which must have had 3 inches of aperture as a Gregorian. The Gregorianreflector he initially used, for the first catalog version, had an 810mm (32-inch) focal length and an aperture of 162mm (6.4 inches). 5) Newtonian reflector of 4.5-feet (1.46m) focal length and a magnification of 60×, with 8 inches of aperture. This telescope belonged to the Royal Observatory, but Messier was allowed to use it occasionally, as for detailed observations of M 42 and Comet Halley.
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• M 75: Messier believed that he saw individual stars, Méchain reported just a nebula. And indeed, at magnitude 14.6, even the brightest individual stars are far below the perception limit of Messier’s and Méchain’s telescopes. • M 76: as above, Messier reported individual stars, Méchain just a nebula, but the object does not contain any stars brighter than 13th magnitude. Messier could not have seen them. • M 77: as above, Messier took it for a star cluster, while Méchain saw a nebula. In fact, it is a galaxy with a star-like core. • M 78: Messier saw a star cluster with nebulosity, Méchain a nebula with two bright cores. In reality, this is a reflection nebula with two embedded 9th-magnitude stars. For some other objects, Messier’s observational impressions are obviously so vague that he was misled in determining the type of object. Some discrepancies are so large that several modern astronomers have started to doubt whether Messier saw the respective objects at all. One is the Trifid Nebula M 20, which was classified by Messier as a star cluster. Another example is the aforementioned M 57, where Messier believed the Ring Nebula consisted of stars. A different case is M 16. Here, Messier correctly reported a star cluster with nebulous background, but the real nebula is too faint to have been seen by him. It was discovered photographically in the early twentieth century and received a separate designation as IC 4703. However, this may well be a misjudgment of Messier’s visual talents. We may simply be underestimating the light pollution of nocturnal Paris in the eighteenth century. In fact, at that time, Paris was the largest city in the world with a population of 800,000. There are contemporary descriptions of how chaotic the situation was in the large city. Smoke from oven-heated houses, numerous factories and open fires must have created air pollution considerably worse than today’s, scattering and absorbing more starlight. In addition, all public streets and squares were floodlit by oil-burning lamps every winter (October to March) from 1667 until their gradual destruction after the French revolution in 1789. Not surprisingly, the Royal Observatory (founded in 1667) was given a location outside the city, but the Observatory of the Navy was quite central. Hence, Messier’s night sky may have been much worse than we imagine. Messier’s notes themselves give an impression of the severity of light pollution in his day. Assuming a loss of transmission due to uncoated optics of 30% in his 3.5-inch Dollond refractor would lead to an equivalent aperture of 3 inches or 75mm. Such an instrument has a limiting magnitude of about 12 under dark rural skies (naked-eye limit 6.5). As analyzed above, the faintest stars Messier could actually see with this instrument were around 11.0, which leads to a naked eye limit of about 5.5 – similar to a severely polluted suburban sky today. Messier’s telescopic limit with the 6.4-inch Gregorian was at about th 11 magnitude, as he could see individual stars in M 4 at 10.8, but not resolve any other globular cluster. We know that the metal mirrors of Messier’s time had a very poor reflectance and losses totalled up to 50%, effectively downsizing the 6.4-inch to a mere 4.5-inch. This instrument would have a limiting magnitude of about 11, if the naked eye limit was only 4.5 – which is equivalent to observing conditions frequently occurring today in large cities.
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Another point to consider is the illumination used by Messier for his star-charts, his notes and his reticle. He had no electric light at his disposal; everything was lit with oil lamps and torches – the thought of which would invoke horror in any visual observer today. So, compared to many modern deep-sky observers, Messier was seriously disadvantaged in terms of instrumentation, and yet he also had to deal with the light pollution many of us experience. With this in mind, we can understand Messier’s mistakes and award him the credit he deserves.
Statistics of the Messier objects When Charles Messier observed the objects that eventually made up his famous catalog, his visual impressions only allowed him to distinguish between “amas d’étoiles” (star clusters) and “nebuleuse” (nebulae). By our modern methods of astrophysics, we can finally classify Messier’s objects according to their physical categories. His catalog contains: • • • • • •
6 Galactic nebulae 28 Open clusters 4 Planetary nebulae 29 Globular clusters 40 Galaxies 3 other objects
In this list, M 8 has been counted as an open (star) cluster, because Messier noted the star cluster as the main object. M 16, of which Messier could not see the surrounding nebulosity, is registered as a star cluster, while the nebula has its separate catalog designation (IC 4703). M 20, regarded by Messier as a star cluster like the other two objects, is classified as a galactic nebula today. But in reality, modern classification is still a bit ad hoc. For example, the galactic nebulae M 17, M 20, and M 42 are best known for their dust-enshrouded, young star clusters in the process of formation, only hidden in visual light. M 45, the Pleiades, is the brightest Messier object with a total magnitude of 1.2. This bright star cluster is visible to the naked eye even under a light-polluted sky. The status of the faintest Messier object is shared by M 76, M 91, and M 98, all at a total magnitude of only 10.1. The largest in angular size of all Messier objects is undoubtedly the Andromeda Galaxy (M 31) at 4° × 1°. Under a very dark, transparent sky, a visual size of as much as 5° has been reported. However, in absolute terms, the galaxy M 101 is the physically largest object of the Messier catalog. With a diameter of 184,000 light-years, it reaches 1½ times the size of our neighbor galaxy M 31 and almost twice the size of our own galaxy. M 31 just happens to be the nearest large spiral galaxy, at only 2.5 million light-years distance, which is what makes it look so large. By contrast, the object with the smallest angular diameter is M 40, a pair of stars separated by only 49", followed by M 73 and M 76 at just 1' in diameter. Planetary nebula M 76 appears to be, if its supposed
distance of 2550 light-years is correct, the physically smallest Messier object with a diameter of 0.7 light-years, while both M 40 and M 73 are not physical objects at all. 69 objects in Messier’s list are members of our own Milky Way and thus relatively near: only 430 light-years separate us from the Pleiades, but we are 78,000 light-years from globular cluster M 75, the farthest galactic Messier object. The 41 extragalactic objects are all galaxies, with one exception: M 54 is a globular cluster of the near dwarf galaxy SagDEG. The most distant Messier object is the galaxy M 109 with considerable 67.5 million light-years – that is 157,000× more distant than M 45! On an age scale, the Messier objects cover an even larger range than their distances do. The youngest object, M 1, was created less than 1000 years ago by a supernova, recorded by historic civilizations in the year 1054. The globular clusters M 69 and M 92 have, by contrast, an age of 12 to 13 thousand million years, almost as old as the whole Universe.
The galactic nebulae Galactic nebulae make up a most diverse category, which includes all of the diverse gaseous and dusty nebulae in our galaxy. The Messier catalog contains several star-forming HII regions, a reflection nebula, and a supernova remnant. HII regions contain mostly hydrogen gas that has a very low density by laboratory standards and is ionized by the ultraviolet (UV) light of nearby hot stars. While cool, neutral hydrogen (HI) remains unobservable in visual light, ionized hydrogen (HII) recombines and emits in the Balmer lines of HD at 656nm, and HE at 486nm. From the traces of heavier elements in these gaseous nebulae, we also receive line emission in visual light from doubly ionized oxygen ([OIII], at 501nm and 496nm) and of singly ionized nitrogen ([NII], at 658nm and 655nm). In order to get any nearby or surrounding hydrogen gas to glow, a star must have a sufficiently energetic ultraviolet radiation field. Hence, HII regions are created only by very hot stars of spectral type O and early B. These short-lived, luminous, and massive stars are found only in young star clusters and star-forming regions, which are surrounded by an HII region – gas that was not consumed by the star formation
53
talog is M 78. Well known but faint are the reflection nebulae around the Pleiades. They do not represent leftover material from the formation of the stars, but rather an unrelated interstellar cloud accidentally passed by the cluster. A rare case consists of the orange nebulae that reflect the light of red supergiant Antares, near M 4 and M 80. A very different type of object is M 1: it is the remnant of a very massive star that was destroyed by a supernova explosion nearly 1000 years ago. Such a catastrophic event is caused by the gravitational collapse of a massive stellar core, following the exhaustion of its nuclear fuel. It leaves behind a chaotically structured shell of material expanding at up to 20,000 km/s, the nebulous supernova remnant, and a super-dense stellar remnant, a neutron star. It is so dense because, during the gravitational collapse, electrons and protons have merged to neutrons, which are now packed as densely as in an atomic nucleus. The enormous reduction in size, in combination with conservation of angular momentum, has, for the M 1 neutron star, led to a super-fast rotation of 33 Members Age times per second. The magnetic field has been compressed 332 100 Myr by a factor of 10 million. Its 1000 500–700 Myr axis is inclined with respect 750 220 Myr to the rotation axis, and as 60 240–480 Myr the intense field lines move >300 0.1 Myr rapidly through the surroun64 80–100 Myr ding electron gas, a bluish 117 30–100 Myr glimmer of synchrotron ra94 225 Myr diation is created. This is the 220 100 Myr same process as observed by 177 300 Myr physicists in large electron 70 190 Myr accelerator rings. The neutron 165 300 Myr star in M 1 is also known as >120 0.3– 0.4 Myr a pulsar from radio observa2700 150 Myr tions. 2050 100 Myr M 1 lies at a distance of 6200 light-years, which is al500 3700 Myr most five times further than ? 400 Myr to the star-forming nebulae ? 150–250 Myr M 42, M 43, and M 78, all part 229 4–6 Myr of the Orion cloud, and grea105 4–8 Myr ter still than the distances to 40 50 Myr M 8 and M 17.
process, often found to survive in the dense, dusty and opaque interior of the cloud. Here, globules are found: dense, round dark nebulae that contain a proto-star. M 42 is a good example of how the energetic ionizing radiation of the luminous hot stars forms an opening in the inner cloud of dust and gas by radiation-driven erosion, while the youngest part of the star cluster still remains hidden inside. M 20, by contrast, appears more spherical, as there is only one dominating hot star in its center, which creates an HII region equally distributed around it. Stars with cooler photospheres may be very luminous, but their weak ultraviolet radiation may not be sufficient to ionize the surrounding gas. Instead, if dust is present, their light can be reflected off the dust particles and scattered. This is what we see as a reflection nebula. Since the scattering process is more efficient in blue light, these nebulae appear bluish – like the part of M 20, which contrasts with the ionized, red H-emitting part. The only pure reflection nebula in the Messier ca-
The open clusters of the Messier catalog No.
Magnitude
Angular size
Distance
Physical size
M 45
1.5
2°
425 Ly
15 Ly
M 44
3.1
1.2º
610 ly
15 ly
M7
3.3
80'
980 ly
23 ly
M 39
4.6
30'
1010 ly
9 ly
M 42
?
3'
1300 ly
4 ly
M6
4.2
20'
1590 ly
10 ly
M 47
4.4
30'
1600 ly
14 ly
M 34
5.2
35'
1630 ly
17 ly
M 25
4.6
30'
2020 ly
17 ly
M 23
5.5
35'
2050 ly
20 ly
M 41
4.5
40'
2260 ly
26 ly
M 48
5.8
30'
2510 ly
22 ly
M 20
8.5
20'
2660 ly
15 ly
M 35
5.1
28'
2710 ly
22 ly
M 50
5.9
15'
2870 ly
13 ly
M 67
6.9
25'
2960 ly
21 ly
M 93
6.2
24'
3380 ly
23 ly
M 38
6.4
15'
3480 ly
15 ly
M 26
6.6
10'
3740 ly
10 ly
M 21
5.9
18'
3930 ly
20 ly
M 18
6.9
5'
4220 ly
6 ly
M 36
6.0
12'
4300 ly
15 ly
M8
5.8
7'
4310 ly
9 ly
M 46
6.1
20'
4480 ly
26 ly
500
500 Myr
M 37
5.6
25'
4510 ly
33 ly
2000
500 Myr
M 52
6.9
16'
4630 ly
22 ly
6000
25–165 Myr
M 29
8.0
8'
5160 ly
12 ly
69
90 Myr
M 16
6.0
21'
5600 ly
35 ly
376
2–6 Myr
M 17
?
5'
5910 ly
10 ly
2200
1 Myr
M 11
5.8
13'
6120 ly
23 ly
2900
250 Myr
M 103
7.4
6'
7150 ly
17 ly
77
178
>130
20–40 Myr 2.3 Myr
16–25 Myr
in order of their distances, based on: Kharchenko, N. V. et al.: Astrophysical parameters of Galactic open clusters, Astronomy and Astrophysics 438, 1163 (2005)
54
The open clusters Open (star) clusters, loose accumulations of a few dozen to several thousand stars, are the result of a star formation process that once consumed a dense cloud of interstellar material. Initially hidden in-
side the gaseous cloud (M 17, M 42), the hottest O-type giants emerge first (M 8, M 16). Depending on its total mass and on the gravitational interactions with its environment, a star cluster can hold together for several million to even a few thousand million years. But with time, the cluster stars are lost to the galactic disk. Large molecular clouds can create a number of neighboring star clusters of similar age that form an association. M 36 and M 37, for example, belong to the Auriga-OB-association. OB indicates that the hottest spectral types are still present in this young formation. These luminous stars burn faster and the most massive members very soon explode as supernovae. The other massive stars evolve to become red giants. M 37, M 50, and M 103 are examples of open clusters that already contain their first red giants. Hence, the youngest star clusters can be recognized by the very hot and massive stars among their members. A good example is 2-million-year-old M 8 with 9 Sgr. Even younger are the clusters still in the process of formation in M 42, M 20, and M 17. At the other extreme is M 67 with an age of 3.7 thousand million years. To a large extent, it owes its long survival to its sparsely populated galactic environment. The poorest Messier clusters are M 18 and M 39 with only 40 and 60 confirmed member stars each. They are also the smallest clusters of the Messier catalog at only about 10 light-years in diameter. The richest open cluster in the Messier catalog is probably M 52 (about 6000 stars), followed by M 11 (2900) and M 35 (2700). M 11, together with M 37, is also among the largest open clusters in general. With a diameter of 50 light-years, each is the size of a small globular cluster. Plotting the open clusters in the galactic plane around the Sun at their proper distances, we obtain a pattern that coincides with the spiral arms of our galaxy. Most of the nearer open clusters, beginning with the Pleiades at a distance of only 430 light-years, are in the Orion arm. The Sun itself lies in the inner edge of that same arm. Towards the galactic center, a number of clusters mark the Sagittarius arm. It hosts, for example, M 11, M 16, and M 8. In the opposite direction lies the Perseus arm with M 103 (at a distance of 7200 light-years) and h & F Persei. Even further away (12,000 light-years) towards the galactic edge is NGC 2158, which in the sky appears to be a close neighbor of M 35.
The planetary nebulae Messier’s catalog contains only four planetary nebulae. These objects are a by-product of the creation of white dwarfs. This is the evolutionary fate of most stars, except the most massive ones which will undergo a supernova explosion. A planetary nebula, by contrast, is formed by a gradual process: in the final, very cool supergiant stages with a highly compressed stellar core, the star’s surface gravity becomes extremely low. Under these conditions, a cool, slow, and relatively dense wind or “superwind” removes all of the remaining outer stellar layers in the final twenty- to fifty-thousand years. With the exposure of a now “naked” hot core, a much thinner, hot and very fast wind starts. As it pushes outwards, accompanied by ionizing ultraviolet radiation, an ionized shell is formed inside the cool, still slowly expanding circumstellar gas and dust – a glowing nebula with emission lines, not unlike an HII region, but for very different physical reasons. The higher densities in the shells of planetary nebulae favor [OIII] line emission over the hydrogen Balmer lines (i.e., HD, HE – the intensity ratio can
Trümpler classification of open clusters This classification scheme was introduced in 1930 by Robert J. Trümpler. Born in Switzerland, he emigrated to the USA early in the twentieth century. He thought that clusters of similar appearance (same Trümpler class) would be physically alike (e.g., have the same size). If so, the distances to open clusters could be estimated, and they could be used to trace galactic structure. The Trümpler classification has four parameters, which describe:
Appearance I II III IV
with strong central concentration, standing out well. cluster with weak central concentration, standing out well. cluster without any noticeable concentration, stars distributed thinly but evenly, standing out well. cluster, which does not stand out well from the background but appears like a concentration in the star field.
Brightness distribution of cluster stars 1 2 3
most cluster stars have nearly the same brightness. moderate brightness distribution of the stars. cluster composed of bright and faint stars, typically a few very bright and several moderately bright stars standing out from a large group of faint stars.
Number of cluster stars p m r
poor cluster with less than 50 stars. moderately rich cluster with 50 to 100 stars. rich cluster with more than 100 stars.
Additional indicators e u n
elongated. asymmetrical. contains nebulosity.
According to this scheme, M 45 has been classified as I3m, M 37 as I2r and M 39 as III2m. Today the Trümpler classification system is hardly ever used, since it is very subjective and depends on the observing method. Modern distance measurements and the determination of cluster age now rely on precise photometry of cluster stars and their colors, and a quantitative interpretation by computer models of stars and their evolution.
55
be twice as high. The ionizing power of the hot wind and ultraviolet radiation fades on a timescale of about 10,000 years. At the same time, the now aged planetary nebula begins to disperse, just like the last breath of a “dying” star. Planetary nebulae reach sizes of only a few light-years. In the Messier catalog, they span about the range of 0.7 (M 76) to 3.5 (M 97) light-years. Exact sizes and distances, however, are notoriously difficult to assess for these objects.
The globular clusters Sun
ly
ly
ly
ly
Globular clusters are dynamically stable objects, due to their large total mass. Their name relates to their mostly spherical form. About 150 of these objects are known in the Galaxy, which they surround in a widespread halo. However, that number is dwarfed by the quantity of globular clusters surrounding other galaxies, e.g., 16,000 around the giant galaxy M 87. Looking at the distribution of our globular clusters in the sky, there is a remarkable concentration towards the galactic center – the inner halo. These globular clusters are frequently found in, or crossing, our galactic disk while orbiGalactic center ting the galactic center. The nearest globular clusters have distances comparable to those of open cluThe distribution of open clusters and galactic nebulae of the Messier catalog on the galactic sters. M 4 at about 5600 light-years, for plane, within a radius of 10,000 light-years around the Sun. The nearest spiral arms are example, is nearer to us than M 11. Towards indicated. the galactic center, however, we not only see globular clusters in front of it (like M 22), but also next to it (like M 28) or on its far side (M 72). Towards M when a globular cluster has undergone a core collapse (by dynamical 75 at a distance of 78,000 light-years, our view crosses two-thirds of instability and transfer of kinetic energy out of the core region) are the galactic diameter. super-densities of up to 100,000 stars per cubic light-year reached. A A special case among the globular clusters is M 54. It is not a ga- visual measure of the degree of concentration is the classification of lactic object but belongs to the small dwarf galaxy SagDEG. Hence, at globular clusters into class I (extremely compact) to XII (very loose), a distance of 85,000 light-years, this is the most distant globular clu- analogous to the “Trümpler classes” for open clusters. While this ster of the Messier catalog. scheme has no relevance to astrophysical research any more, it is a The physical size and the mass of globular clusters differ greatly. very useful one for the visual amateur observer. The most concentrated The smallest example is M 71: with 40,000 solar masses and fewer than globular cluster in the Messier catalog is M 2 (II), the loosest examples 100,000 stars, it is not much larger than the largest open clusters. At are M 55 and M 71 (XI). Galactic globular clusters have ages of about 10 to 13 thousand the other extreme are M 19 and M 54, each with several million stars and a mass of 1.5 million solar masses, approximately that of a dwarf million years – about 100 times older than most open clusters. Having lost their interstellar matter, globular clusters cannot form new stars. galaxy. Photographs, in particular, give the impression of very high star Hence, all their member stars are very old, which is why they show densities in globular clusters. In reality, however, there are between 10 the elemental composition of earlier stages of the Universe. Elements and 1000 stars per cubic light-year at their centers – which means that heavier than hydrogen and helium can form only by the central nuclethe average distance between stars is still 0.1 to 0.5 light-years. Only ar processes of stars and supernova explosions, and they are dispersed
56
into the interstellar medium by supernovae and stellar winds to feed new star formation. Hence, globular clusters give testimony of the early Universe when heavy elements were much less abundant, and that distinguishes them from all other stellar clusters. Low abundance of heavy elements and low stellar mass bring about a special group of variables, typical for globular clusters: the pulsating RR Lyrae stars. Lacking a static equilibrium between radiation pressure and gravity, these stars oscillate over the course of a few hours and show brightness variations of about 0.5 to 2 magnitudes. In addition, there are other types of variables in globular clusters. The record holder is M 3 with 274 known variable stars, while in M 10 only four variables have been discovered so far. Luminous stars of spectral type O and B are not found in globular clusters, because these stars “die” very young. Oddly enough, a few blue stars are found in globular clusters: “blue stragglers.” Hence, these must have been formed recently – supposedly by the merging of close, old binary stars. Some globular clusters even host pulsars. The record holder in the Messier catalog is M 62 with six of them.
The galaxies
The planetary nebulae of the Messier catalog No.
Magnitude
Angular size
Distance
Physical diameter
Age
M 76
10.1
67"
2550 ly
0.7 ly
?
M 57
8.8
86" × 62"
2300 ly
0.9 ly
10,000–20,000 years
M 97
9.9
170"
4140 ly
3.5 ly
6000–12,000 years
M 27
7.4
8.4' × 6.1'
1150 ly
3.0 ly
~ 9000 years
The globular clusters of the Messier catalog No.
Magnitude
Angular size
M4
5.8
35'
M 22
5.1
33'
Distance 5640 ly 10,440 ly
Physical diameter Mass 57 ly 100 ly
Variables
100 × 103 M
65
3
78
3
500 × 10 M
M 71
8.0
7'
18,330 ly
40 ly
40 × 10 M
23
M 55
6.3
19'
19,300 ly
110 ly
250 × 103 M
40
M 12
6.8
14'
20,760 ly
85 ly
3
5
3
250 × 10 M
M 10
6.6
19'
24,750 ly
140 ly
200 × 10 M
4
M 13
5.7
21'
25,890 ly
160 ly
600 × 103 M
40, Pulsar
M5
5.7
20'
26,620 ly
150 ly
3
143
3
800 × 10 M
M 92
6.5
14'
27,140 ly
110 ly
400 × 10 M
20
M 107
7.8
13'
27,370 ly
105 ly
200 × 103 M
23
M 56
8.4
7'
27,390 ly
55 ly
3
14
3
200 × 10 M
M 30
7.3
12'
29,460 ly
100 ly
300 × 10 M
13
M3
5.9
19'
34,170 ly
190 ly
800 × 103 M
274
3
M 28
6.8
10'
34,480 ly
100 ly
500 × 10 M
19, Pulsar
M 70
7.8
8'
34,770 ly
80 ly
200 × 103 M
>10
M 62
6.7
11'
34,930 ly
110 ly
M 68
7.6
11'
36,580 ly
120 ly
M 69
7.7
10'
36,920 ly
110 ly
3
1000 × 10 M ? 300 × 103 M
>200, 6 Pulsars 42 13
An older technical term for galaxies was “extraM 15 6.0 18' 39,010 ly 200 ly 131 450 × 103 M galactic nebulae.” However, that does not reflect 3 their true nature as distant milky ways in their M2 6.4 16' 40,850 ly 190 ly 30 900 × 10 M own right, with many thousand millions of stars, 7 M 79 7.7 6' 45,000 ly 80 ly 400 × 103 M 3 thousands of open clusters, globular clusters, and M 19 6.7 14' 45,000 ly 180 ly 1500 × 10 M 8 HII regions. In the nearest galaxies, the memM9 7.6 11' 46,090 ly 150 ly 16 300 × 103 M bers of our Local Group, we are able to observe M 80 7.3 9' 48,260 ly 125 ly 10 400 × 103 M such individual objects. The Andromeda Galaxy 3 M 14 7.6 11' 55,620 ly 180 ly 1200 × 10 M 68 (M 31) in particular is a nice example of a large M 72 9.2 6' 58,510 ly 100 ly 51 200 × 103 M spiral galaxy. It has a diameter of about 160,000 3 M 53 7.7 13' 61,270 ly 230 ly 67, Pulsar 750 × 10 M light-years and 300 to 400 thousand million solar 3 46 M 75 8.6 7' 77,840 ly 160 ly 500 × 10 M masses. By contrast our other neighbor, M33, has M 54 7.2 12' 84,650 ly 300 ly 1500 × 103 M 211 only about one tenth of the mass of M 31. in order of their distances, based on: Recio-Blanco, A. et al.: Distance of 72 Galactic globular clusters, Astronomy and Astrophysics, 432, 851 (2005) With increasing distance from us, groups and clusters of galaxies become more obvious in the sky. M 81 and M 82 are 12 million light-years light-years. It is 26 times farther away than M 31, 770 times more diaway, M 51 is 27 million light-years. These form two small, widely stant than M 54, and 150,000 times farther than M 45. scattered galaxy groups with other, smaller galaxies, mostly dwarfs. Dwarf galaxies like M 32, which is tied by gravity to its mother gaA large and dense gathering of galaxies, by contrast, is the center of laxy M 31, may have diameters of only a few thousand light-years. At the Virgo galaxy cluster at a distance of 45 to 62 million light-years. the other extreme, M 101 measures about 185,000 light-years, almost About 2500 galaxies are packed within a diameter of 10 to 15 milli- twice as much as our own Milky Way. Any accurate assessment of gaon light-years, 14 of them are found in the Messier catalog. The most laxy diameters, however, is made difficult by their inclination from a distant example of all Messier galaxies is M 109 at about 67.5 million perfect face-on view.
57
Spectral types of stars and stellar evolution Very generally speaking, all stars are built the same way: in a dense, hot core, hydrogen fuses to helium. The core is surrounded by outer layers that provide the right conditions to transport the energy outside, by radiation or by convection. Depending on mass, however, stars can have very different temperatures (from 3000K to 100,000K) and densities in their photospheres. The conditions in these outermost layers can be determined by a detailed spectral analysis of the star’s light. Although developed 120 years ago, the spectral classification scheme below is still used today by professional astronomers, because it immediately gives an approximate temperature value.
11000K Rigel
7500K
6000K
4500K
5
Ib Supergiants Spica
Every spectral class is divided into 10 subclasses from 0 to 9. For very cool, red stars, there are two additional, special classes: 10000
Antares 5
4 II Bright giants
0
Mira
Capella A III Giants
Vega Sirius A
Ma
in
+5
Aldebaran A
4
IV Subgiants seq
uen
1
ce
1
Sun Dwarfs
Subdwarfs +10
Absolute magnitude
0,01
White dwarfs
Barnard´s Star O
B
A
F
G
K
M
Spectral type
The Hertzsprung-Russell diagram. The location of the main sequence and evolution tracks of two stars are plotted: A) the Sun – 1: present state; yellow main-sequence “dwarf,” hydrogen-burning in core, 2: first giant branch; hydrogenburning in shell, 3: “helium flash,” 4: helium-burning in core, 5: asymptotic giant branch; helium- and hydrogen-burning shells, mass loss by a “cool wind” leaves a white dwarf. B) massive star – 1: blue main-sequence star, hydrogenburning in core, 2: hydrogen-burning in shell, 3: smooth onset of helium-burning, 4: “blue loop;” helium-burning in core, 5: red supergiant; helium- and hydrogen-burning shells, later carbon-burning in core, mass loss by a “cool wind.”
58
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